CODEWITHSUNDEEP
c++stringarguments
GeorgieF
GeorgieF

Reputation: 2737

How to pass string type arguments to c++ methods

I am a C++ noob, fiddling with the following problem for some hours now. Hopefully, someone can enlighten me.

I had a cpp file with content like so:

test.cpp file content

#include <iostream>
#include <exception>
#include <stdlib.h>
#include <string.h>
using std::cin; using std::endl;
using std::string;


string foobar(string bar) {
  return "foo" + bar;
}

int main(int argc, char* argv[])
{
    string bar = "bar";
    System::convCout << "Foobar: " << foobar(bar) << endl;
}

This one compiles and runs well. Now I'd like to put foobar into an external library:

mylib.h file content

string foobar(string bar);

mylib.cpp file content

#include <string.h>
using std::cin; using std::endl;
using std::string;

string foobar(string bar) {
  return "foo" + bar;
}

test.cpp file content

#include <iostream>
#include <exception>
#include <stdlib.h>
#include "mylib.h"

int main(int argc, char* argv[])
{
    string bar = "bar";
    System::convCout << "Foobar: " << foobar(bar) << endl;
}

I adjusted my Makefile, so that test.cpp compiles and links mylib, but I always encounter the error: 

test.cpp::8 undefined reference to `foobar(std::string)

How do I have to handle string arguments? My attempts seems to be completely wrong here.

Regards Felix

Upvotes: 0

Views: 157

Answers (1)

juanchopanza
juanchopanza

Reputation: 227618

The C++ standard library type std::string is in the header string. To use it, you must include <string>, not <string.h>. Your mylib.h should look something like

#ifndef MYLIB_H
#define MYLIB_H

#include <string>

std::string foobar(std::string bar);

#endif

and your mylib.cpp should include it:

#include "mylib.h"

std::string foobar(std::string bar) {
  return "foo" + bar;
}

Note that it may be unnecessary to pass bar by value. Looking at your code, a const reference might do.

Upvotes: 1

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