php内置函数分析之trim()

官方手册中：

类似函数还有两个：ltrim() 和 rtrim()。分别处理字符串的左侧、右侧。

trim()的具体实现位于：ext/standard/string.c

/* {{{ proto string trim(string str [, string character_mask])
   Strips whitespace from the beginning and end of a string */
PHP_FUNCTION(trim)
{
    php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, );
}
/* }}} */

/* {{{ php_do_trim
 * Base for trim(), rtrim() and ltrim() functions.
 */
static void php_do_trim(INTERNAL_FUNCTION_PARAMETERS, int mode)
{
    zend_string *str;
    zend_string *what = NULL;

    ZEND_PARSE_PARAMETERS_START(, )
        Z_PARAM_STR(str)
        Z_PARAM_OPTIONAL
        Z_PARAM_STR(what)
    ZEND_PARSE_PARAMETERS_END();

    ZVAL_STR(return_value, php_trim(str, (what ? ZSTR_VAL(what) : NULL), (what ? ZSTR_LEN(what) : ), mode));
}
/* }}} */

具体实现：

 /* {{{ php_trim()
  * mode 1 : trim left
  * mode 2 : trim right
  * mode 3 : trim left and right
  * what indicates which chars are to be trimmed. NULL->default (' \t\n\r\v\0')
  */
 PHPAPI zend_string *php_trim(zend_string *str, char *what, size_t what_len, int mode)
 {
     const char *c = ZSTR_VAL(str);
     size_t len = ZSTR_LEN(str);
     register size_t i;
     size_t trimmed = ;
     char mask[];

     if (what) {
         if (what_len == ) {
             char p = *what;
             if (mode & ) {
                 for (i = ; i < len; i++) {
                     if (c[i] == p) {
                         trimmed++;
                     } else {
                         break;
                     }
                 }
                 len -= trimmed;
                 c += trimmed;
             }
             if (mode & ) {
                 if (len > ) {
                     i = len - ;
                     do {
                         if (c[i] == p) {
                             len--;
                         } else {
                             break;
                         }
                     } while (i-- != );
                 }
             }
         } else {
             php_charmask((unsigned char*)what, what_len, mask);

             if (mode & ) {
                 for (i = ; i < len; i++) {
                     if (mask[(unsigned char)c[i]]) {
                         trimmed++;
                     } else {
                         break;
                     }
                 }
                 len -= trimmed;
                 c += trimmed;
             }
             if (mode & ) {
                 if (len > ) {
                     i = len - ;
                     do {
                         if (mask[(unsigned char)c[i]]) {
                             len--;
                         } else {
                             break;
                         }
                     } while (i-- != );
                 }
             }
         }
     } else {
         if (mode & ) {
             for (i = ; i < len; i++) {
                 if ((unsigned char)c[i] <= ' ' &&
                     (c[i] == ' ' || c[i] == '\n' || c[i] == '\r' || c[i] == '\t' || c[i] == '\v' || c[i] == '\0')) {
                     trimmed++;
                 } else {
                     break;
                 }
             }
             len -= trimmed;
             c += trimmed;
         }
         if (mode & ) {
             if (len > ) {
                 i = len - ;
                 do {
                     if ((unsigned char)c[i] <= ' ' &&
                         (c[i] == ' ' || c[i] == '\n' || c[i] == '\r' || c[i] == '\t' || c[i] == '\v' || c[i] == '\0')) {
                         len--;
                     } else {
                         break;
                     }
                 } while (i-- != );
             }
         }
     }

     if (ZSTR_LEN(str) == len) {
         return zend_string_copy(str);
     } else {
         return zend_string_init(c, len, );
     }
 }
 /* }}} */

ltrim()、rtrim() 或 trim()的参数二（what）存在时进入15行处的分支，参数二不存在时进入68行处的分支。

没有参数二时，会去除空格、"\t"、"\n"、"\r"、"\0"、"\v"

即：(unsigned char)c[i] <= ' ' && (c[i] == ' ' || c[i] == '\n' || c[i] == '\r' || c[i] == '\t' || c[i] == '\v' || c[i] == '\0')

存在参数二时，会去除参数二中指定的字符。

其中函数 php_charmask() 用于处理 trim("abc123456fjsklsf", "a..z") 中 字符范围 a...z

 static inline int php_charmask(unsigned char *input, size_t len, char *mask)
 {
     unsigned char *end;
     unsigned char c;
     int result = SUCCESS;

     memset(mask, , );
     for (end = input+len; input < end; input++) {
         c=*input;
         if ((input+ < end) && input[] == '.' && input[] == '.'
                 && input[] >= c) {
             memset(mask+c, , input[] - c + );
             input+=;
         } else if ((input+ < end) && input[] == '.' && input[] == '.') {
             /* Error, try to be as helpful as possible:
                (a range ending/starting with '.' won't be captured here) */
             if (end-len >= input) { /* there was no 'left' char */
                 php_error_docref(NULL, E_WARNING, "Invalid '..'-range, no character to the left of '..'");
                 result = FAILURE;
                 continue;
             }
             if (input+ >= end) { /* there is no 'right' char */
                 php_error_docref(NULL, E_WARNING, "Invalid '..'-range, no character to the right of '..'");
                 result = FAILURE;
                 continue;
             }
             if (input[-] > input[]) { /* wrong order */
                 php_error_docref(NULL, E_WARNING, "Invalid '..'-range, '..'-range needs to be incrementing");
                 result = FAILURE;
                 continue;
             }
             /* FIXME: better error (a..b..c is the only left possibility?) */
             php_error_docref(NULL, E_WARNING, "Invalid '..'-range");
             result = FAILURE;
             continue;
         } else {
             mask[c]=;
         }
     }
     return result;
 }

第二个参数是字符范围的时候，源码中并没有严格限制成 a..z 这样的格式。

总的流程就是，待处理的字符串左侧（或右侧）逐字符去匹配是否在将要去除的字符中（第二个参数设置的字符 或者 默认的那6个字符），

如果字符匹配到则进行下一个比较，否则中断匹配查找。返回余下字符串。