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; } 

C++ FAQ Lite

[39.2] How do I convert a std::string to a number?

https://isocpp.org/wiki/faq/misc-technical-issues#convert-string-to-num

Let me add my vote for boost::lexical_cast

#include <boost/lexical_cast.hpp> int val = boost::lexical_cast<int>(strval) ; 

It throws bad_lexical_cast on error.

Use atoi

Perhaps I am misunderstanding the question, by why exactly would you not want to use atoi? I see no point in reinventing the wheel.

Am I just missing the point here?