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const char * strchr ( const char * str, int character );
char * strchr ( char * str, int character );
Returns a pointer to the first occurrence of character in the C string str.
The terminating null-character is considered part of the C string. Therefore, it can also be located in order to retrieve a pointer to the end of a string.
Return: 第一次出现位置，出错则返回NULL
strch.c源码
char * strchr (s, c_in) const char *s; int c_in; { const unsigned char *char_ptr; const unsigned long int *longword_ptr; unsigned long int longword, magic_bits, charmask; unsigned char c; c = (unsigned char) c_in; /* Handle the first few characters by reading one character at a time. Do this until CHAR_PTR is aligned on a longword boundary. */ for (char_ptr = (const unsigned char *) s; ((unsigned long int) char_ptr & (sizeof (longword) - 1)) != 0; ++char_ptr) if (*char_ptr == c) return (void *) char_ptr; else if (*char_ptr == ‘\0‘) return NULL; /* All these elucidatory comments refer to 4-byte longwords, but the theory applies equally well to 8-byte longwords. */ longword_ptr = (unsigned long int *) char_ptr; /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits the "holes." Note that there is a hole just to the left of each byte, with an extra at the end:
总结： 1. strchr查找是以循环比较所查找字符
2. 字符 char默认是 1 个字节，若是宽字符则需令处理
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原文地址：http://www.cnblogs.com/iclk/p/4279118.html
