How to find substring from string?

In C, use the strstr() standard library function:

const char *str = "/user/desktop/abc/post/";
const int exists = strstr(str, "/abc/") != NULL;

Take care to not accidentally find a too-short substring (this is what the starting and ending slashes are for).

Use std::string and find.

std::string str = "/user/desktop/abc/post/";
bool exists = str.find("/abc/") != std::string::npos;