How to use C++11 std::stoi with gcc? [duplicate]

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How to convert a number to string and vice versa in C++

I am using Qt Creator 2.5.0 and gcc 4.7 (Debian 4.7.2-4). I added "QMAKE_CXXFLAGS += -std=c++11" to .pro file. Everything seems to be OK, I used C++11 std::for_each and so on. But when I included "string" header and wanted to use stoi, i got the following error:

performer.cpp:336: error: 'std::string' has no member named 'stoi'

I found some questions related to MinGW and one more, to Eclipse CDT and they had their answers. But I use Linux, why it is NOT working here?

Are you trying something like string.stoi(...)? It should be std::stoi(string, ...);. — zch
– zch, Commented Nov 27, 2012 at 17:48
@KillianDS, come on.. stoi is mentioned on that post only on an "update" answer. It doesn't even give an example. This question is about how to use it, was a syntax problem. — aldo.roman.nurena
– aldo.roman.nurena, Commented Nov 28, 2012 at 18:44
@aldo.roman.nurena actually the exact title of this question was about how to use std::stoi (more specifically how you call it), which is answered there. — KillianDS
– KillianDS, Commented Nov 28, 2012 at 18:53

aldo.roman.nurena · Accepted Answer · 2012-11-27 17:47:29Z

4

#include <iostream> #include <string> int main() { std::string test = "45"; int myint = stoi(test); std::cout << myint << '\n'; }

or

#include <iostream> #include <string> using namespace std int main() { string test = "45"; int myint = stoi(test); cout << myint << '\n'; }

look at http://en.cppreference.com/w/cpp/string/basic_string/stol

answered Nov 27, 2012 at 17:47

aldo.roman.nurena

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3 Comments

Razorfever Over a year ago

Thank you very much. It seems to be quite stupid question, but anyway, I hope it will help someone else not to ask it in future :D

Chad Skeeters Over a year ago

When I compile with g++ -std=c++11, stoi doesn't need the namespace specified like your top example. cppreference.com lists it has being in the std namespace, but has the same example you posted here. How might someone know which members of the std namespace don't need the std qualification?

AnT stands with Russia Over a year ago

@Chad Skeeters: Without using namespace std, all members of std namespace need std qualification, unless they can be found by argument-dependent name lookup (ADL). ADL is the reason this code compiles without using namespace std and without std::. It is a rather extensive topic, which the margins of this comment are too narrow to contain. Search it, there is a lot of info on the Net.

Mike Seymour · Accepted Answer · 2012-11-27 18:31:37Z

std::stoi is a function at namespace scope, taking a string as its argument:

std::string s = "123"; int i = std::stoi(s);

From the error message, it looks like you expect it to be a member of string, invoked as s.stoi() (or perhaps std::string::stoi(s)); that is not the case. If that's not the problem, then please post the problematic code so we don't need to guess what's wrong with it.

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