c 字符串处理函数----strtok 源码

/*** *strtok.c - tokenize a string with given delimiters * * Copyright (c) Microsoft Corporation. All rights reserved. * *Purpose: * defines strtok() - breaks string into series of token * via repeated calls. * *******************************************************************************/ #include #include #ifdef _SECURE_VERSION #include #else /* _SECURE_VERSION */ #include #endif /* _SECURE_VERSION */ /*** *char *strtok(string, control) - tokenize string with delimiter in control * *Purpose: * strtok considers the string to consist of a sequence of zero or more * text tokens separated by spans of one or more control chars. the first * call, with string specified, returns a pointer to the first char of the * first token, and will write a null char into string immediately * following the returned token. subsequent calls with zero for the first * argument (string) will work thru the string until no tokens remain. the * control string may be different from call to call. when no tokens remain * in string a NULL pointer is returned. remember the control chars with a * bit map, one bit per ascii char. the null char is always a control char. * *Entry: * char *string - string to tokenize, or NULL to get next token * char *control - string of characters to use as delimiters * *Exit: * returns pointer to first token in string, or if string * was NULL, to next token * returns NULL when no more tokens remain. * *Uses: * *Exceptions: * *******************************************************************************/ #ifdef _SECURE_VERSION #define _TOKEN *context #else /* _SECURE_VERSION */ #define _TOKEN ptd->_token #endif /* _SECURE_VERSION */ #ifdef _SECURE_VERSION char * __cdecl strtok_s ( char * string, const char * control, char ** context ) #else /* _SECURE_VERSION */ char * __cdecl strtok ( char * string, const char * control ) #endif /* _SECURE_VERSION */ { unsigned char *str; const unsigned char *ctrl = control; unsigned char map[32]; int count; #ifdef _SECURE_VERSION /* validation section */ _VALIDATE_RETURN(context != NULL, EINVAL, NULL); _VALIDATE_RETURN(string != NULL || *context != NULL, EINVAL, NULL); _VALIDATE_RETURN(control != NULL, EINVAL, NULL); /* no static storage is needed for the secure version */ #else /* _SECURE_VERSION */ _ptiddata ptd = _getptd(); #endif /* _SECURE_VERSION */ /* Clear control map */ for (count = 0; count < 32; count++) map[count] = 0; /* Set bits in delimiter table */ do { map[*ctrl >> 3] |= (1 << (*ctrl & 7)); } while (*ctrl++); /* Initialize str */ /* If string is NULL, set str to the saved * pointer (i.e., continue breaking tokens out of the string * from the last strtok call) */ if (string) str = string; else str = _TOKEN; /* Find beginning of token (skip over leading delimiters). Note that * there is no token iff this loop sets str to point to the terminal * null (*str == '/0') */ while ( (map[*str >> 3] & (1 << (*str & 7))) && *str ) str++; string = str; /* Find the end of the token. If it is not the end of the string, * put a null there. */ for ( ; *str ; str++ ) if ( map[*str >> 3] & (1 << (*str & 7)) ) { *str++ = '/0'; break; } /* Update nextoken (or the corresponding field in the per-thread data * structure */ _TOKEN = str; /* Determine if a token has been found. */ if ( string == str ) return NULL; else return string; }