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| <h3 class="section">5.2 String and Array Conventions</h3> |
| |
| <p>This chapter describes both functions that work on arbitrary arrays or |
| blocks of memory, and functions that are specific to null-terminated |
| arrays of characters and wide characters. |
| |
| <p>Functions that operate on arbitrary blocks of memory have names |
| beginning with ‘<samp><span class="samp">mem</span></samp>’ and ‘<samp><span class="samp">wmem</span></samp>’ (such as <code>memcpy</code> and |
| <code>wmemcpy</code>) and invariably take an argument which specifies the size |
| (in bytes and wide characters respectively) of the block of memory to |
| operate on. The array arguments and return values for these functions |
| have type <code>void *</code> or <code>wchar_t</code>. As a matter of style, the |
| elements of the arrays used with the ‘<samp><span class="samp">mem</span></samp>’ functions are referred |
| to as “bytes”. You can pass any kind of pointer to these functions, |
| and the <code>sizeof</code> operator is useful in computing the value for the |
| size argument. Parameters to the ‘<samp><span class="samp">wmem</span></samp>’ functions must be of type |
| <code>wchar_t *</code>. These functions are not really usable with anything |
| but arrays of this type. |
| |
| <p>In contrast, functions that operate specifically on strings and wide |
| character strings have names beginning with ‘<samp><span class="samp">str</span></samp>’ and ‘<samp><span class="samp">wcs</span></samp>’ |
| respectively (such as <code>strcpy</code> and <code>wcscpy</code>) and look for a |
| null character to terminate the string instead of requiring an explicit |
| size argument to be passed. (Some of these functions accept a specified |
| maximum length, but they also check for premature termination with a |
| null character.) The array arguments and return values for these |
| functions have type <code>char *</code> and <code>wchar_t *</code> respectively, and |
| the array elements are referred to as “characters” and “wide |
| characters”. |
| |
| <p>In many cases, there are both ‘<samp><span class="samp">mem</span></samp>’ and ‘<samp><span class="samp">str</span></samp>’/‘<samp><span class="samp">wcs</span></samp>’ |
| versions of a function. The one that is more appropriate to use depends |
| on the exact situation. When your program is manipulating arbitrary |
| arrays or blocks of storage, then you should always use the ‘<samp><span class="samp">mem</span></samp>’ |
| functions. On the other hand, when you are manipulating null-terminated |
| strings it is usually more convenient to use the ‘<samp><span class="samp">str</span></samp>’/‘<samp><span class="samp">wcs</span></samp>’ |
| functions, unless you already know the length of the string in advance. |
| The ‘<samp><span class="samp">wmem</span></samp>’ functions should be used for wide character arrays with |
| known size. |
| |
| <p><a name="index-wint_005ft-471"></a><a name="index-parameter-promotion-472"></a>Some of the memory and string functions take single characters as |
| arguments. Since a value of type <code>char</code> is automatically promoted |
| into an value of type <code>int</code> when used as a parameter, the functions |
| are declared with <code>int</code> as the type of the parameter in question. |
| In case of the wide character function the situation is similarly: the |
| parameter type for a single wide character is <code>wint_t</code> and not |
| <code>wchar_t</code>. This would for many implementations not be necessary |
| since the <code>wchar_t</code> is large enough to not be automatically |
| promoted, but since the ISO C<!-- /@w --> standard does not require such a |
| choice of types the <code>wint_t</code> type is used. |
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