Run the following code:

$tag = "$tag"; $text = rtrim($tag, ", "); print_r($text);Copy the code

What we might have expected was an Internet product, but it turned out to be an Internet product. Why is that?

The principle of

Trim function documentation

string trim ( string $str [, string $character_mask = " \t\n\r\0\x0B" ] )Copy the code

$character_mask = char; $character_mask = char; $character_mask = char; Such as:

echo ltrim("bcdf","abc"); // dfCopy the code

The string_print_char function in demo is described as follows:, consists of three bytes 0xe3 0x80 0x81, and pin consists of three bytes 0xe5 0x93 0x81. Therefore, when performing rtrim, 0x81 will be removed by byte alignment, resulting in garbled characters.

Source lite demo

View PHP7 source code, and then extract the following small demo, convenient for everyone to learn together, in fact, PHP source code learning is not difficult, a little bit of progress every day.

// // main.c // Trim // // Created by Zhou Mengkang 2017/10/18. // Copyright © 2017 Zhou Mengkang. All rights reserved. // #include <stdio.h> #include <stdlib.h> #include <string.h> void string_print_char(char *str); void php_charmask(unsigned char *input, size_t len, char *mask); char *ltrim(char *str,char *character_mask); char *rtrim(char *str,char *character_mask); int main(int argc, char const *argv[]) { printf("%s\n",ltrim("bcdf","abc")); String_print_char (" products "); // e5 93 81 string_print_char(", "); // e3 80 81 printf("%s\n",rtrim(" %s\n", ","); return 0; } char *ltrim(char *str,char *character_mask) { char *res; char mask[256]; register size_t i; int trimmed = 0; size_t len = strlen(str); php_charmask((unsigned char*)character_mask, strlen(character_mask), mask); for (i = 0; i < len; i++) { if (mask[(unsigned char)str[i]]) { trimmed++; } else { break; } } len -= trimmed; str += trimmed; res = (char *) malloc(sizeof(char) * (len+1)); memcpy(res,str,len); return res; } char *rtrim(char *str,char *character_mask) { char *res; char mask[256]; register size_t i; size_t len = strlen(str); php_charmask((unsigned char*)character_mask, strlen(character_mask), mask); if (len > 0) { i = len - 1; do { if (mask[(unsigned char)str[i]]) { len--; } else { break; } } while (i-- ! = 0); } res = (char *) malloc(sizeof(char) * (len+1)); memcpy(res,str,len); return res; } void string_print_char(char *str) { unsigned long l = strlen(str); for (int i=0; i < l; i++) { printf("%02hhx\t",str[i]); } printf("\n"); } void php_charmask(unsigned char *input, size_t len, char *mask) { unsigned char *end; unsigned char c; memset(mask, 0, 256); for (end = input+len; input < end; input++) { c = *input; mask[c]= 1; }}Copy the code

PHP7 related source code

PHP_FUNCTION(trim)
{
    php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 3);
}
PHP_FUNCTION(rtrim)
{
    php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 2);
}
PHP_FUNCTION(ltrim)
{
    php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 1);
}Copy the code

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));
}Copy the code

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 = 0; char mask[256]; if (what) { if (what_len == 1) { char p = *what; if (mode & 1) { for (i = 0; i < len; i++) { if (c[i] == p) { trimmed++; } else { break; } } len -= trimmed; c += trimmed; } if (mode & 2) { if (len > 0) { i = len - 1; do { if (c[i] == p) { len--; } else { break; } } while (i-- ! = 0); } } } else { php_charmask((unsigned char*)what, what_len, mask); if (mode & 1) { for (i = 0; i < len; i++) { if (mask[(unsigned char)c[i]]) { trimmed++; } else { break; } } len -= trimmed; c += trimmed; } if (mode & 2) { if (len > 0) { i = len - 1; do { if (mask[(unsigned char)c[i]]) { len--; } else { break; } } while (i-- ! = 0); } } } } else { if (mode & 1) { for (i = 0; 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 & 2) { if (len > 0) { i = len - 1; 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-- ! = 0); } } } if (ZSTR_LEN(str) == len) { return zend_string_copy(str); } else { return zend_string_init(c, len, 0); }}Copy the code

/* {{{ php_charmask * Fills a 256-byte bytemask with input. You can specify a range like 'a.. z', * it needs to be incrementing. * Returns: FAILURE/SUCCESS whether the input was correct (i.e. no range errors) */ static inline int php_charmask(unsigned char *input, size_t len, char *mask) { unsigned char *end; unsigned char c; int result = SUCCESS; memset(mask, 0, 256); for (end = input+len; input < end; input++) { c=*input; if ((input+3 < end) && input[1] == '.' && input[2] == '.' && input[3] >= c) { memset(mask+c, 1, input[3] - c + 1); input+=3; } else if ((input+1 < end) && input[0] == '.' && input[1] == '.') { /* 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+2 >= 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[-1] > input[2]) { /* 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]=1; } } return result; }}}} / * * /Copy the code