docs/src/features.md

Sun, 31 Dec 2023 14:29:46 +0100

author
Mike Becker <universe@uap-core.de>
date
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child 819
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-rw-r--r--

declare cx_compare_func in compare.h - fixes #344

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1 ---
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2 title: UCX Features
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3 ---
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4
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5 <div id="modules">
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6
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7 ------------------------ ------------------------- ------------------- ---------------------------------
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8 [Allocator](#allocator) [String](#string) [Buffer](#buffer) [Memory&nbsp;Pool](#memory-pool)
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9 [Iterator](#iterator) [Collection](#collection) [List](#list) [Map](#map)
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10 [Utilities](#utilities)
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11 ------------------------ ------------------------- ------------------- ---------------------------------
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12
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13 </div>
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14
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15 ## Allocator
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16
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17 *Header file:* [allocator.h](api/allocator_8h.html)
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18
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19 The UCX allocator provides an interface for implementing an own memory allocation mechanism.
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20 Various function in UCX provide an additional alternative signature that takes an allocator as
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21 argument. A default allocator implementation using the stdlib memory management functions is
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22 available via the global symbol `cxDefaultAllocator`.
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23
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24 If you want to define your own allocator, you need to initialize the `CxAllocator` structure
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25 with a pointer to an allocator class (containing function pointers for the memory management
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26 functions) and an optional pointer to an arbitrary memory region that can be used to store
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27 state information for the allocator. An example is shown below:
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28
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29 ```c
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30 struct my_allocator_state {
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31 size_t total;
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32 size_t avail;
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33 char mem[];
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34 };
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35
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36 static cx_allocator_class my_allocator_class = {
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37 my_malloc_impl,
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38 my_realloc_impl, // all these functions are somewhere defined
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39 my_calloc_impl,
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40 my_free_impl
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41 };
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42
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43 CxAllocator create_my_allocator(size_t n) {
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44 CxAllocator alloc;
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45 alloc.cl = &my_allocator_class;
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46 alloc.data = calloc(1, sizeof(struct my_allocator_state) + n);
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47 return alloc;
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48 }
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49 ```
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50
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51 ## String
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52
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53 *Header file:* [string.h](api/string_8h.html)
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54
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55 UCX strings come in two variants: immutable (`cxstring`) and mutable (`cxmutstr`).
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56 The functions of UCX are designed to work with immutable strings by default but in situations where it is necessary,
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57 the API also provides alternative functions that work directly with mutable strings.
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58 Functions that change a string in-place are, of course, only accepting mutable strings.
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59
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60 When you are using UCX functions, or defining your own functions, you are sometimes facing the "problem",
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61 that the function only accepts arguments of type `cxstring` but you only have a `cxmutstr` at hand.
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62 In this case you _should not_ introduce a wrapper function that accepts the `cxmutstr`,
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63 but instead you should use the `cx_strcast()` function to cast the argument to the correct type.
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64
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65 In general, UCX strings are **not** necessarily zero-terminated. If a function guarantees to return zero-terminated
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66 string, it is explicitly mentioned in the documentation of the respective function.
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67 As a rule of thumb, you _should not_ pass the strings of a UCX string structure to another API without explicitly
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68 ensuring that the string is zero-terminated.
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69
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70 ## Buffer
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71
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72 *Header file:* [buffer.h](api/buffer_8h.html)
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73
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74 Instances of this buffer implementation can be used to read from or write to memory like you would do with a stream.
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75 This allows the use of `cx_stream_copy()` (see [Utilities](#utilities)) to copy contents from one buffer to another,
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76 or from a file or network streams to the buffer and vice-versa.
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77
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78 More features for convenient use of the buffer can be enabled, like automatic memory management and automatic
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79 resizing of the buffer space.
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80
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81 Since UCX 3.0, the buffer also supports automatic flushing of contents to another stream (or buffer) as an alternative
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82 to automatically resizing the buffer space.
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83 Please refer to the API doc for the fields prefixed with `flush_` to learn more.
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84
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85 ## Memory Pool
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86
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87 *Header file:* [mempool.h](api/mempool_8h.html)
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88
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89 A memory pool is providing an allocator implementation that automatically deallocates the memory upon its destruction.
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90 It also allows you to register destructor functions for the allocated memory, which are automatically called before
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91 the memory is deallocated.
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92 Additionally, you may also register _independent_ destructor functions within a pool in case some external library
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93 allocated memory for you, which should be destroyed together with this pool.
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94
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95 Many UCX features support the use of an allocator.
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96 The [strings](#string), for instance, provide several functions suffixed with `_a` that allow specifying an allocator.
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97 You can use this to keep track of the memory occupied by dynamically allocated strings and cleanup everything with
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98 just a single call to `cxMempoolDestroy()`.
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99
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100 The following code illustrates this on the example of reading a CSV file into memory.
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101 ```C
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102 #include <stdio.h>
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103 #include <cx/mempool.h>
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104 #include <cx/linked_list.h>
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105 #include <cx/string.h>
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106 #include <cx/buffer.h>
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107 #include <cx/utils.h>
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108
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109 typedef struct {
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110 cxstring column_a;
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111 cxstring column_b;
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112 cxstring column_c;
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113 } CSVData;
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114
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115 int main(void) {
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116 CxMempool* pool = cxBasicMempoolCreate(128);
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117
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118 FILE *f = fopen("test.csv", "r");
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119 if (!f) {
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120 perror("Cannot open file");
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121 return 1;
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122 }
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123 // close the file automatically at pool destruction
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124 cxMempoolRegister(pool, f, (cx_destructor_func) fclose);
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125
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126 // create a buffer using the memory pool for destruction
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127 CxBuffer *content = cxBufferCreate(NULL, 256, pool->allocator, CX_BUFFER_AUTO_EXTEND);
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128
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129 // read the file into the buffer and turn it into a string
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130 cx_stream_copy(f, content, (cx_read_func) fread, (cx_write_func) cxBufferWrite);
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131 fclose(f);
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132 cxstring contentstr = cx_strn(content->space, content->size);
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133
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134 // split the string into lines - use the mempool for allocating the target array
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135 cxstring* lines;
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136 size_t lc = cx_strsplit_a(pool->allocator, contentstr,
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137 CX_STR("\n"), SIZE_MAX, &lines);
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138
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139 // skip the header and parse the remaining data into a linked list
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140 // the nodes of the linked list shall also be allocated by the mempool
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141 CxList* datalist = cxLinkedListCreate(pool->allocator, NULL, sizeof(CSVData));
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142 for (size_t i = 1 ; i < lc ; i++) {
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143 if (lines[i].length == 0) continue;
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144 cxstring fields[3];
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145 size_t fc = cx_strsplit(lines[i], CX_STR(";"), 3, fields);
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146 if (fc != 3) {
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147 fprintf(stderr, "Syntax error in line %zu.\n", i);
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148 cxMempoolDestroy(pool);
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149 return 1;
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150 }
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151 CSVData data;
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152 data.column_a = fields[0];
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153 data.column_b = fields[1];
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154 data.column_c = fields[2];
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155 cxListAdd(datalist, &data);
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156 }
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157
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158 // iterate through the list and output the data
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159 CxIterator iter = cxListIterator(datalist);
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160 cx_foreach(CSVData*, data, iter) {
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161 printf("Column A: %.*s | "
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162 "Column B: %.*s | "
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163 "Column C: %.*s\n",
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164 (int)data->column_a.length, data->column_a.ptr,
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165 (int)data->column_b.length, data->column_b.ptr,
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166 (int)data->column_c.length, data->column_c.ptr
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167 );
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168 }
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169
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170 // cleanup everything, no manual free() needed
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171 cxMempoolDestroy(pool);
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172
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173 return 0;
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174 }
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175 ```
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176
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177 ## Iterator
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178
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179 *Header file:* [iterator.h](api/iterator_8h.html)
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180
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181 In UCX 3 a new feature has been introduced to write own iterators, that work with the `cx_foreach` macro.
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182 In previous UCX releases there were different hard-coded foreach macros for lists and maps that were not customizable.
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183 Now, creating an iterator is as simple as creating a `CxIterator` struct and setting the fields in a meaningful way.
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184
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185 You do not always need all fields in the iterator structure, depending on your use case.
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186 Sometimes you only need the `index` (for example when iterating over simple lists), and other times you will need the
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187 `slot` and `kv_data` fields (for example when iterating over maps).
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188
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189 Usually an iterator is not mutating the collection it is iterating over.
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190 In some programming languages it is even disallowed to change the collection while iterating with foreach.
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191 But sometimes it is desirable to remove an element from the collection while iterating over it.
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192 This is, what the `CxMutIterator` is for.
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193 The only differences are, that the `mutating` flag is `true` and the `src_handle` is not const.
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194 On mutating iterators it is allowed to call the `cxFlagForRemoval()` function, which instructs the iterator to remove
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195 the current element from the collection on the next call to `cxIteratorNext()` and clear the flag afterward.
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196 If you are implementing your own iterator, it is up to you to implement this behavior in your `next` method, or
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197 make the implementation of the `flag_removal` method always return `false`.
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198
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199 ## Collection
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200
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201 *Header file:* [collection.h](api/collection_8h.html)
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202
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203 Collections in UCX 3 have several common features.
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204 If you want to implement an own collection data type that uses the same features, you can use the
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205 `CX_COLLECTION_MEMBERS` macro at the beginning of your struct to roll out all members a usual UCX collection has.
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206 ```c
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207 struct my_fancy_collection_s {
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208 CX_COLLECTION_MEMBERS
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209 struct my_collection_data_s *data;
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210 };
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211 ```
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212 Based on this structure, this header provides some convenience macros for invoking the destructor functions
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213 that are part of the basic collection members.
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214 The idea of having destructor functions within a collection is that you can destroy the collection _and_ the
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215 contents with one single function call.
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216 When you are implementing a collection, you are responsible for invoking the destructors at the right places, e.g.
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217 when removing (and deleting) elements in the collection, clearing the collection, or - the most prominent case -
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218 destroying the collection.
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219
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220 You can always look at the UCX list and map implementations if you need some inspiration.
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221
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222 ## List
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223
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224 *Header file:* [list.h](api/list_8h.html)
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225
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226 This header defines a common interface for all list implementations, which is basically as simple as the following
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227 structure.
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228 ```c
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229 struct cx_list_s {
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230 CX_COLLECTION_MEMBERS // size, capacity, etc.
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231 cx_list_class const *cl; // The list class definition
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232 };
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233 ```
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234 The actual structure contains one more class pointer that is used when wrapping a list into a pointer-aware list
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235 with `cxListStorePointers()`. What this means, is that - if you want to implement your own list structure - you
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236 only need to cover the case where the list is storing copies of your objects.
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237
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238 UCX comes with two common list implementations (linked list and array list) that should cover most use cases.
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239 But if you feel the need to implement an own list, the only thing you need to do is to define a struct where
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240 `struct cx_list_s`, and set an appropriate list class that implements the functionality.
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241 It is strongly recommended that this class is shared among all instances of the same list type, because otherwise
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242 the `cxListCompare` function cannot use the optimized implementation of your class and will instead fall back to
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243 using iterators to compare the contents element-wise.
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244
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245 ### Linked List
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246
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247 *Header file:* [linked_list.h](api/linked__list_8h.html)
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248
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249 On top of implementing the list interface, this header also defines several low-level functions that
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250 work with arbitrary structures.
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251 Low-level functions, in contrast to the high-level list interface, can easily be recognized by their snake-casing.
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252 The function `cx_linked_list_at`, for example, implements a similar functionality like `cxListAt`, but operates
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253 on arbitrary structures.
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254 The following snippet shows how it is used.
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255 All other low-level functions work similarly.
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256 ```c
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257 struct node {
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258 node *next;
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259 node *prev;
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260 int data;
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261 };
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262
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263 const ptrdiff_t loc_prev = offsetof(struct node, prev);
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264 const ptrdiff_t loc_next = offsetof(struct node, next);
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265 const ptrdiff_t loc_data = offsetof(struct node, data);
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266
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267 struct node a = {0}, b = {0}, c = {0}, d = {0};
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268 cx_linked_list_link(&a, &b, loc_prev, loc_next);
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269 cx_linked_list_link(&b, &c, loc_prev, loc_next);
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270 cx_linked_list_link(&c, &d, loc_prev, loc_next);
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271
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272 cx_linked_list_at(&a, 0, loc_next, 2); // returns pointer to c
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273 ```
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274
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275 ### Array List
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276
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277 *Header file:* [array_list.h](api/array__list_8h.html)
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278
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279 Since low-level array lists are just plain arrays, there is no need for such many low-level functions as for linked
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280 lists.
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281 However, there is one extremely powerful function that can be used for several complex tasks: `cx_array_copy`.
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282 The full signature is shown below:
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283 ```c
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284 enum cx_array_copy_result cx_array_copy(
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285 void **target,
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286 size_t *size,
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287 size_t *capacity, // optional
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288 size_t index,
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289 void const *src,
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290 size_t elem_size,
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291 size_t elem_count,
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292 struct cx_array_reallocator_s *reallocator // optional
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293 );
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294 ```
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295 The `target` argument is a pointer to the target array pointer.
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296 The reason for this additional indirection is that - given that you provide a `reallocator` - this function writes
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297 back the pointer to the possibly reallocated array.
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298 THe next two arguments are pointers to the `size` and `capacity` of the target array.
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299 Tracking the capacity is optional.
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300 If you do not specify a pointer for the capacity, automatic reallocation of the array is entirely disabled (i.e. it
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301 does not make sense to specify a `reallocator` then).
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302 In this case, the function cannot copy more than `size-index` elements and if you try, it will return
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303 `CX_ARRAY_COPY_REALLOC_NOT_SUPPORTED` and do nothing.
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304
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305 On a successful invocation, the function copies `elem_count` number of elements, each of size `elem_size` from
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306 `src` to `*target` and uses the `reallocator` to extend the array when necessary.
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307 Finally, the size, capacity, and the pointer to the array are all updated and the function returns
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308 `CX_ARRAY_COPY_SUCCESS`.
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309
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310 The third, but extremely rare, return code is `CX_ARRAY_COPY_REALLOC_FAILED` and speaks for itself.
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311
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312 A few things to note:
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313 * `*target` and `src` can point to the same memory region, effectively copying elements within the array with `memmove`
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314 * `*target` does not need to point to the start of the array, but `size` and `capacity` always start counting from the
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315 position, `*target` points to - in this scenario, specifying a `reallocator` is forbidden for obvious reasons
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316 * `index` does not need to be within size of the current array, if `capacity` is specified
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317 * `index` does not even need to be within the capacity of the array, if `reallocator` is specified
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318
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319
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320 ## Map
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321
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322 *Header file:* [map.h](api/map_8h.html)
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323
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324 Similar to the list interface, the map interface provides a common API for implementing maps.
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325 There are some minor subtle differences, though.
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326
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327 First, the `remove` method is not always a destructive removal.
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328 Instead, the last argument is a Boolean that indicates whether the element shall be destroyed or returned.
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329 ```c
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330 void *(*remove)(CxMap *map, CxHashKey key, bool destroy);
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331 ```
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332 When you implement this method, you are either supposed to invoke the destructors and return `NULL`,
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333 or just remove the element from the map and return it.
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334
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335 Secondly, the iterator method is a bit more complete. The signature is as follows:
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336 ```c
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337 CxIterator (*iterator)(CxMap const *map, enum cx_map_iterator_type type);
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338 ```
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339 There are three map iterator types: for values, for keys, for pairs.
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340 Depending on the iterator type requested, you need to create an iterator with the correct methods that
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341 return the requested thing.
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342 There are no automatic checks to enforce this - it's completely up to you.
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343 If you need inspiration on how to do that, check the hash map implementation that comes with UCX.
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344
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345 ### Hash Map
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346
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347 *Header file:* [hash_map.h](api/hash__map_8h.html)
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348
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349 UCX provides a basic hash map implementation with a configurable amount of buckets.
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350 If you do not specify the number of buckets, a default of 16 buckets will be used.
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351 You can always rehash the map with `cxMapRehash()` to change the number of buckets to something more efficient,
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352 but you need to be careful, because when you use this function you are effectively locking into using this
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353 specific hash map implementation, and you would need to remove all calls to this function when you want to
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354 exchange the concrete map implementation with something different.
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355
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356 ## Utilities
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357
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358 *Header file:* [utils.h](api/utils_8h.html)
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359
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360 UCX provides some utilities for routine tasks. Most of them are simple macros, like e.g. the `cx_for_n()` macro,
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361 creating a `for` loop counting from zero to (n-1) which is extremely useful to traverse the indices of
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362 an array.
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363
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364 But the most useful utilities are the *stream copy* functions, which provide a simple way to copy all - or a
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365 bounded amount of - data from one stream to another. Since the read/write functions of a UCX buffer are
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366 fully compatible with stream read/write functions, you can easily transfer data from file or network streams to
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367 a UCX buffer or vice-versa.
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368
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369 The following example shows, how easy it is to read the contents of a file into a buffer:
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370 ```c
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371 FILE *inputfile = fopen(infilename, "r");
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372 if (inputfile) {
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373 CxBuffer fbuf;
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374 cxBufferInit(&fbuf, NULL, 4096, NULL, CX_BUFFER_AUTO_EXTEND);
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375 cx_stream_copy(inputfile, &fbuf,
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376 (cx_read_func) fread,
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377 (cx_write_func) cxBufferWrite);
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378 fclose(inputfile);
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379
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380 // ... do something meaningful with the contents ...
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381
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382 cxBufferDestroy(&fbuf);
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383 } else {
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384 perror("Error opening input file");
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385 if (fout != stdout) {
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386 fclose(fout);
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387 }
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388 }
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389 ```
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390
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391 ### Printf Functions
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392
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393 *Header file:* [printf.h](api/printf_8h.html)
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394
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395 In this utility header you can find `printf()`-like functions that can write the formatted output to an arbitrary
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396 stream (or UCX buffer, resp.), or to memory allocated by an allocator within a single function call.
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397 With the help of these convenience functions, you do not need to `snprintf` your string to a temporary buffer anymore,
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398 plus you do not need to worry about too small buffer sizes, because the functions will automatically allocate enough
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399 memory to contain the entire formatted string.
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400
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401 ### Compare Functions
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402
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403 *Header file:* [compare.h](api/compare_8h.html)
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404
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405 This header file contains a collection of compare functions for various data types.
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406 Their signatures are designed to be compatible with the `cx_compare_func` function pointer type.

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