你可以尝试使用find函数:

string str ("There are two needles in this haystack.");
string str2 ("needle");

if (str.find(str2) != string::npos) {
//.. found.
} 

如果不想使用标准库函数，下面是一种解决方案。

#include <iostream>
#include <string>

bool CheckSubstring(std::string firstString, std::string secondString){
    if(secondString.size() > firstString.size())
        return false;

    for (int i = 0; i < firstString.size(); i++){
        int j = 0;
        // If the first characters match
        if(firstString[i] == secondString[j]){
            int k = i;
            while (firstString[i] == secondString[j] && j < secondString.size()){
                j++;
                i++;
            }
            if (j == secondString.size())
                return true;
            else // Re-initialize i to its original value
                i = k;
        }
    }
    return false;
}

int main(){
    std::string firstString, secondString;

    std::cout << "Enter first string:";
    std::getline(std::cin, firstString);

    std::cout << "Enter second string:";
    std::getline(std::cin, secondString);

    if(CheckSubstring(firstString, secondString))
        std::cout << "Second string is a substring of the frist string.\n";
    else
        std::cout << "Second string is not a substring of the first string.\n";

    return 0;
}

从c++ 23开始，你可以使用std::string::contains

#include <string>

const auto haystack = std::string("haystack with needles");
const auto needle = std::string("needle");

if (haystack.contains(needle))
{
    // found!
}

你可以尝试使用find函数:

string str ("There are two needles in this haystack.");
string str2 ("needle");

if (str.find(str2) != string::npos) {
//.. found.
} 

使用std::string::find如下所示:

if (s1.find(s2) != std::string::npos) {
    std::cout << "found!" << '\n';
}

注意:如果s2是s1的子字符串，则打印"found!"， s1和s2都是std::string类型。

你可以试试这个

string s1 = "Hello";
string s2 = "el";
if(strstr(s1.c_str(),s2.c_str()))
{
   cout << " S1 Contains S2";
}