C library function -strstr()

C Standard Library - <string.h>

Description

C Library Functionschar *strstr(const char *haystack, const char *needle) In the stringhaystackFind the first occurrence of a string inneedlethe position, not including the terminating character\0。

strstr() is a string handling function in the C standard library, used to find the first occurrence of a substring in a string.

Declaration

Below is the declaration of the strstr() function.

char *strstr(const char *haystack, const char *needle);

The strstr() function is used to find the first occurrence of the substring needle in the string haystack. If found, it returns a pointer to that location; if not found, it returns NULL.

Parameter

  • haystack-- The main string to be searched.
  • needle-- the substring to be searched for.

Return Value

Returns a pointer to the first occurrence of needle in haystack. If needle is not found in haystack, returns NULL.

Example

The following example demonstrates the usage of the strstr() function.

Example 1

#include <stdio.h> #include <string.h> int main() { const char haystack[20] = "EXAMPLE"; const char needle[10] = "NOOB"; char *ret; ret = strstr(haystack, needle); printf("The substring is: %s\n", ret); return(0); }

Let us compile and run the above program, which will produce the following result:

子字符串是： NOOB

Example 2

#include <stdio.h>
#include <string.h>

int main() {
    const char *haystack = "Hello, world! This is a test string.";
    const char *needle = "world";

    // Find needle in haystack
    char *result = strstr(haystack, needle);

    if (result != NULL) {
        printf("Substring found: %s\n", result);
    } else {
        printf("Substring not found.\n");
    }

    return 0;
}

Code explanation:

  • strstr()function fromhaystackstart searching from the beginning ofneedle, until finding a matching substring or reachinghaystackthe end.

  • ifneedleis an empty string (""），strstr()will returnhaystackthe starting address of.

  • strstr()is case-sensitive. If you need a case-insensitive search, you can usestrcasestr()(non-standard function, may require specific library support).

Output result:

Substring found: world! This is a test string.

C Standard Library - <string.h>

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