Convert std::string to integer

Question

I'm trying to convert a std::string stored in a std::vector to an integer and pass it to a function as a parameter.

This is a simplified version of my code:

vector <string> record;
functiontest(atoi(record[i].c_str));

My error is as follows:

error: argument of type ‘const char* (std::basic_string<char, std::char_traits<char>, std::allocator<char> >::)()const’ does not match ‘const char*’

How can I do this?

You need to *call* it, but there are many better methods than `atoi`. — chris, Sep 27 '12 at 19:07
Possible duplicate of [How can I convert a std::string to int?](https://stackoverflow.com/questions/7663709/how-can-i-convert-a-stdstring-to-int) — user202729, Jan 09 '19 at 02:04

score 44 · Accepted Answer · answered Sep 27 '12 at 19:37

44

With C++11:

int value = std::stoi(record[i]);

answered Sep 27 '12 at 19:37

Pete Becker

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Quite helpful. For lower than C++11, is there any solid example? – Md Mahbubur Rahman Mar 19 '14 at 04:57
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**Reader Beware:** If you aren't 100% sure the input to `std::stoi` will **always be a valid integer**, you'll need to set up a `try/catch` for `std::invalid_argument`. – CodeMouse92 Apr 16 '16 at 00:01
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And also for `std::out_of_range`. – ebk Sep 12 '17 at 08:27

score 11 · Answer 2 · answered Sep 27 '12 at 19:07

11

record[i].c_str

is not the same as

record[i].c_str()

You can actually get this from the error message: the function expects a const char*, but you're providing an argument of type const char* (std::basic_string<char, std::char_traits<char>, std::allocator<char> >::)()const which is a pointer to a member function of the class std::basic_string<char, std::char_traits<char>, std::allocator<char> > that returns a const char* and takes no arguments.

answered Sep 27 '12 at 19:07

Luchian Grigore

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I can see how the other answer is better, but I don't think this one deserves a downvote... – Luchian Grigore Sep 27 '12 at 19:16

score 11 · Answer 3 · answered Sep 27 '12 at 19:11

11

Use stringstream from standard library. It's cleaner and it's rather C++ than C.

int i3;
std::stringstream(record[i]) >> i3;

answered Sep 27 '12 at 19:11

Indy9000

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@BЈовић Very nice. For C++11 onward though – Indy9000 Sep 27 '12 at 19:16
i guess it must be sloooow as any streams – Oleg Vazhnev May 01 '13 at 20:22
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@Kip9000 in my opinion it's a bad suggestion. `std::stoi` is much better to be used for conversion. it's much clear and much faster. i'm sorry i can't revert downvote as my vote is locked now. – Oleg Vazhnev May 02 '13 at 07:34
@javapowered: That's for C++11 though... As it says in the comments, but before your comment. – Aaron H. Dec 04 '14 at 18:31

score 0 · Answer 4 · answered Sep 15 '15 at 11:39

0

#include <boost/lexical_cast.hpp>

functiontest(boost::lexical_cast<int>(record[i]));

answered Sep 15 '15 at 11:39

Darko Veberic

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Convert std::string to integer

4 Answers4

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