strstr() Function
The strstr() function in C locates the first occurrence of a substring within a larger string and returns a pointer to that position if found, or a null pointer if the substring is not present. It performs a search that stops when the terminating null-character of the main string is encountered.
Syntax of strstr()
const char *strstr(const char *str1, const char *str2);Parameters
| Parameter | Description |
|---|---|
str1 | C string to be scanned. |
str2 | C string containing the sequence of characters to match. |
Return Value
Returns a pointer to the first occurrence of the entire sequence specified in str2 within str1, or a null pointer if the sequence is not present.
Note: The search process stops at the terminating null-character of the main string, meaning that the null terminator is not considered part of the matching sequence.
Examples for strstr()
Example 1: Substring Found
This example demonstrates how to use strstr() to locate a substring that exists within a larger string.
Program
#include <stdio.h>
#include <string.h>
int main() {
const char *haystack = "Hello, welcome to the world of C programming.";
const char *needle = "welcome";
const char *result = strstr(haystack, needle);
if (result != NULL) {
printf("Substring found: %s\n", result);
} else {
printf("Substring not found.\n");
}
return 0;
}Output:
Substring found: welcome to the world of C programming.Example 2: Substring Not Found
This example shows the behavior of strstr() when the substring is absent from the main string.
Program
#include <stdio.h>
#include <string.h>
int main() {
const char *haystack = "Learning C string functions.";
const char *needle = "Python";
const char *result = strstr(haystack, needle);
if (result != NULL) {
printf("Substring found: %s\n", result);
} else {
printf("Substring not found.\n");
}
return 0;
}Output:
Substring not found.