std:: strstr

From cppreference.com
C++
Strings library
Null-terminated byte strings
Defined in header <cstring>
const char * strstr ( const char * haystack, const char * needle ) ;
char * strstr ( char * haystack, const char * needle ) ;

Finds the first occurrence of the byte string needle in the byte string pointed to by haystack . The terminating null characters are not compared.

Parameters

haystack - pointer to the null-terminated byte string to examine
needle - pointer to the null-terminated byte string to search for

Return value

Pointer to the first character of the found substring in haystack , or a null pointer if no such character is found. If needle points to an empty string, haystack is returned.

Example

Run this code 
#include <cstring>
#include <iomanip>
#include <iostream>
 
int main()
{
    const char* str = "Try not. Do, or do not. There is no try.";
    const char* target = "not";
 
    for (const char* result = str; (result = std::strstr(result, target)); ++result)
        std::cout << "Found " << std::quoted(target)
                  << " starting at (" << result - str << "): "
                  << std::quoted(result) << '\n';
}

Output: 

Found "not" starting at (4): "not. Do, or do not. There is no try."
Found "not" starting at (19): "not. There is no try."

See also

finds the first occurrence of the given substring
(public member function of std::basic_string<CharT,Traits,Allocator> )
finds the first occurrence of a wide string within another wide string
(function)
finds the first occurrence of a character
(function)
finds the last occurrence of a character
(function)
C documentation for strstr
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