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A brief discussion on PHP source code three: About strrchr, strstr, stristr functions
A brief discussion on PHP source code three: About strrchr, strstr, stristr functions
This article mainly introduces a brief discussion on PHP source code three: Regarding strrchr, strstr, stristr functions, it has certain reference value. Now I share it with you. Friends in need can refer to it
string strrchr (string haystack, string needle)
Returns the string after the last needle (character) in haystack
If needle is a number, convert this number into the character corresponding to this value
If needle is more than one string, take the first character
If haystack is a number, the number will be converted directly into a string
Call convert_to_string_ex(haystack);
in the program The implementation of this function basically handles some special situations (as above).
At the end, it locates the position where the last needle appears, and returns the string after this position according to the position. If this position does not exist, Same as returning false
string strstr (string haystack, string needle)
This function is similar to strrchr, except that its needle is allowed to be a string, and it searches for the first occurrence of needle. According to This position returns the following string, if it does not exist, it returns FALSE
There are some special details in its code that are worth learning, as shown in the code below.
static inline char *zend_memnstr(char *haystack, char *needle, int needle_len, char *end){
char *p = haystack;
char ne = needle[needle_len-1]; if(needle_len > end-haystack) {
return NULL;
}
end -= needle_len; // 优化细节一，仅查找end-needle_len长度的字符串 while (p <= end) {
// 优化细节二，此处先判断字符串的开头和结尾的字符是否一样，如果一样则再判断整个字符串，提升性能
if ((p = (char *)memchr(p, *needle, (end-p+1))) && ne == p[needle_len-1]) {
if (!memcmp(needle, p, needle_len-1)) {
return p;
}
} if (p == NULL) {
return NULL;
}
p++;
} return NULL;}The above code is the core code implemented by strstr and stristr functions. Function: find the position where needle first appears in haystack
string stristr (string haystack, string needle)
stristr function The function is similar to strstr, except that it is not case-sensitive.
The main difference in the PHP source code implementation is the addition of the operation of converting all strings to lowercase. The program implementation is to add the following code before the search:
php_strtolower(s, s_len);php_strtolower(t, t_len);return php_memnstr(s, t, t_len, s + s_len);
PS: In the process of looking at the source code, I read the previous paragraph of "Recognizing Pointers Again" again, and gained some insights;
Pointers can be added and subtracted not because they are pointers. The rules of addition and subtraction do not belong to variables such as pointers. , but the instinct of the data type address. It is precisely because the address has the ability to add and subtract that the pointer, as a variable storing the address, can perform addition and subtraction operations.
This is the same as integer variables, because integers can be added, subtracted, multiplied and divided, so they can also be added, subtracted, multiplied and divided.
The above is the entire content of this article. I hope it will be helpful to everyone's study. For more related content, please pay attention to the PHP Chinese website!
Related recommendations:
A brief discussion on PHP source code 2: About strlen, strtolower, strtoupper, ord, chr functions
A brief discussion on PHP Source code one: explode and implode functions
The above is the detailed content of A brief discussion on PHP source code three: About strrchr, strstr, stristr functions. For more information, please follow other related articles on the PHP Chinese website!
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