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, 3); } /* }}} */
/* {{{ 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(1, 2) 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) : 0), mode)); } /* }}} */
具体实现：
1 /* {{{ php_trim() 2 * mode 1 : trim left 3 * mode 2 : trim right 4 * mode 3 : trim left and right 5 * what indicates which chars are to be trimmed. NULL->default (' \t\n\r\v\0') 6 */ 7 PHPAPI zend_string *php_trim(zend_string *str, char *what, size_t what_len, int mode) 8 { 9 const char *c = ZSTR_VAL(str); 10 size_t len = ZSTR_LEN(str); 11 register size_t i; 12 size_t trimmed = 0; 13 char mask[256]; 14 15 if (what) { 16 if (what_len == 1) { 17 char p = *what; 18 if (mode & 1) { 19 for (i = 0; i < len; i++) { 20 if (c[i] == p) { 21 trimmed++; 22 } else { 23 break; 24 } 25 } 26 len -= trimmed; 27 c += trimmed; 28 } 29 if (mode & 2) { 30 if (len > 0) { 31 i = len - 1; 32 do { 33 if (c[i] == p) { 34 len--; 35 } else { 36 break; 37 } 38 } while (i-- != 0); 39 } 40 } 41 } else { 42 php_charmask((unsigned char*)what, what_len, mask); 43 44 if (mode & 1) { 45 for (i = 0; i < len; i++) { 46 if (mask[(unsigned char)c[i]]) { 47 trimmed++; 48 } else { 49 break; 50 } 51 } 52 len -= trimmed; 53 c += trimmed; 54 } 55 if (mode & 2) { 56 if (len > 0) { 57 i = len - 1; 58 do { 59 if (mask[(unsigned char)c[i]]) { 60 len--; 61 } else { 62 break; 63 } 64 } while (i-- != 0); 65 } 66 } 67 } 68 } else { 69 if (mode & 1) { 70 for (i = 0; i < len; i++) { 71 if ((unsigned char)c[i] <= ' ' && 72 (c[i] == ' ' || c[i] == '\n' || c[i] == '\r' || c[i] == '\t' || c[i] == '\v' || c[i] == '\0')) { 73 trimmed++; 74 } else { 75 break; 76 } 77 } 78 len -= trimmed; 79 c += trimmed; 80 } 81 if (mode & 2) { 82 if (len > 0) { 83 i = len - 1; 84 do { 85 if ((unsigned char)c[i] <= ' ' && 86 (c[i] == ' ' || c[i] == '\n' || c[i] == '\r' || c[i] == '\t' || c[i] == '\v' || c[i] == '\0')) { 87 len--; 88 } else { 89 break; 90 } 91 } while (i-- != 0); 92 } 93 } 94 } 95 96 if (ZSTR_LEN(str) == len) { 97 return zend_string_copy(str); 98 } else { 99 return zend_string_init(c, len, 0); 100 } 101 } 102 /* }}} */
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
1 static inline int php_charmask(unsigned char *input, size_t len, char *mask) 2 { 3 unsigned char *end; 4 unsigned char c; 5 int result = SUCCESS; 6 7 memset(mask, 0, 256); 8 for (end = input+len; input < end; input++) { 9 c=*input; 10 if ((input+3 < end) && input[1] == '.' && input[2] == '.' 11 && input[3] >= c) { 12 memset(mask+c, 1, input[3] - c + 1); 13 input+=3; 14 } else if ((input+1 < end) && input[0] == '.' && input[1] == '.') { 15 /* Error, try to be as helpful as possible: 16 (a range ending/starting with '.' won't be captured here) */ 17 if (end-len >= input) { /* there was no 'left' char */ 18 php_error_docref(NULL, E_WARNING, "Invalid '..'-range, no character to the left of '..'"); 19 result = FAILURE; 20 continue; 21 } 22 if (input+2 >= end) { /* there is no 'right' char */ 23 php_error_docref(NULL, E_WARNING, "Invalid '..'-range, no character to the right of '..'"); 24 result = FAILURE; 25 continue; 26 } 27 if (input[-1] > input[2]) { /* wrong order */ 28 php_error_docref(NULL, E_WARNING, "Invalid '..'-range, '..'-range needs to be incrementing"); 29 result = FAILURE; 30 continue; 31 } 32 /* FIXME: better error (a..b..c is the only left possibility?) */ 33 php_error_docref(NULL, E_WARNING, "Invalid '..'-range"); 34 result = FAILURE; 35 continue; 36 } else { 37 mask[c]=1; 38 } 39 } 40 return result; 41 }
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。
