C++ String与int转换

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

string int2str(int &i) {
    string s;
    stringstream ss(s);
    ss << i;
    return ss.str();
}

int main(int argc, const char * argv[]) {
    int a = 123;
    string str_a = int2str(a);
    cout<<str_a<<endl;
    return 0;
}