C++:declaring a function that returns string in header file?

Question

In one of my modules, I have a function (changeNum) that returns a string and accepts a parameter that is a string. I tried to declare this function in my header file as following:

std::string changeNum(std::string s);

[and I included the string header file into the header file as well]

but I'm still getting the following error in my header file: "unknown type name 'string'" What do I do?

Here is the whole code: My header file is the following:

#pragma once
#include <string>
std::string changeNum(std::string s);

My module with the function changeNum is defined as the following

#include <string>
string changeNum(string s){
    return s;
}

My header file is the following: #pragma once #include string changeNum(string s); — mechestudent, Apr 19 '20 at 06:06
and my current module function is just this for now: string changeNum(string s) { return s; } — mechestudent, Apr 19 '20 at 06:07
Does this answer your question? [Why is "using namespace std;" considered bad practice?](https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) — L. F., Apr 19 '20 at 06:10
Just modified the question, thank you! Ah got it, thanks for letting me know it is "declare" and not "define." — mechestudent, Apr 19 '20 at 06:14
Have you tried `std::string changeNum(std::string s){ return s; }`? It would be good to make a more complete example of the cpp file. Add the includes and any using statements. — user4581301, Apr 19 '20 at 06:16
I just tried that, and I still am getting the error: "unknown type name: string." — mechestudent, Apr 19 '20 at 06:19
I'm starting from very basic code, so I currently only have those lines in the header file and I have the changeNum in my module, and the only additional #include I have in this module is #include — mechestudent, Apr 19 '20 at 06:21

score 0 · Answer 1 · answered Apr 19 '20 at 07:26

Try it:

Header.h

#pragma once
#include <string>

std::string changeNum(std::string s);

Source.cpp

#include "Header.h"

std::string changeNum(std::string s) {
    return s;
}

main.cpp

#include "Header.h"
#include <iostream>

int main()
{
    std::string sample_str = changeNum("Hello");
    std::cout << sample_str.c_str();
}

Tested on VS and removed #include "pch.h" from aforementioned code.

C++:declaring a function that returns string in header file?

1 Answers1