How do you convert a C++ string to an int? [duplicate]

#include <sstream>

// st is input string
int result;
stringstream(st) >> result;

Use the C++ streams.

std::string       plop("123");
std::stringstream str(plop);
int x;

str >> x;

/* Lets not forget to error checking */
if (!str)
{
     // The conversion failed.
     // Need to do something here.
     // Maybe throw an exception
}

PS. This basic principle is how the boost library lexical_cast<> works.

My favorite method is the boost lexical_cast<>

#include <boost/lexical_cast.hpp>

int x = boost::lexical_cast<int>("123");

It provides a method to convert between a string and number formats and back again. Underneath it uses a string stream so anything that can be marshaled into a stream and then un-marshaled from a stream (Take a look at the >> and << operators).

I have used something like the following in C++ code before:

#include <sstream>
int main()
{
    char* str = "1234";
    std::stringstream s_str( str );
    int i;
    s_str >> i;
}