ld: duplicate symbol

Question

I'm working on a school project and I'm getting some weird errors from Xcode. I'm using TextMate's Command+R function to compile the project. Compilation seems to work okay but linking fails with an error message I don't understand.

ld output:

ld: duplicate symbol text_field(std::basic_istream >&)in /path/final/build/final.build/Release/final.build/Objects-normal/ppc/generics.o and /path/final/build/final.build/Release/final.build/Objects-normal/ppc/main.o collect2: ld returned 1 exit status

Below is my file io_functions.cpp This is the only declaration of text_field in the entire project.

#include <string>
#include <iostream>
#include <iomanip>

using namespace std;

#ifndef ENDF
#define ENDF '|'
#define ENDR '\n'

/**
reads one field from a given input stream
Usage: var = text_field(in)
*/
string text_field(istream &in){
    string s;
    getline(in, s, ENDF);
    return s; 
}

long long_field(istream &in){
    return atol(text_field(in).c_str()); 
}

int int_field(istream &in){
    return atoi(text_field(in).c_str()); 
}

double double_field(istream &in){
    return atof(text_field(in).c_str()); 
}

#endif

What is going wrong? For a number of reasons I don't want to post my project's entire source.

paxdiablo · Accepted Answer · 2009-12-30T02:27:25.710

My first thought was that you're including it twice on the linker command but it appears to be complaining about having the same function in main.o and generics.o.

So it looks like you're including the io_functions.cpp file into the main.cpp and generics.cpp which is a bad idea at the best of times.

You should have a header file (e.g., io_functions.h) that specifies everything contained in io_functions.cpp and include that header file into the other two.

score 6 · Answer 2 · answered Nov 12 '08 at 01:22

6

It sounds like io_functions.cpp is being included twice (once by generics.cpp, once by main.cpp).

answered Nov 12 '08 at 01:22

Josh Kelley

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2

Doesn't #ifndef prevent that from happening? – epochwolf Nov 12 '08 at 01:26
12

Only within the compilation unit - here you have two separate compilation units. The ifndef would stop you from including the file twice in main.cpp. – paxdiablo Nov 12 '08 at 01:27

score 0 · Answer 3 · answered Jan 23 '20 at 07:50

Use "inline" keyword decorate duplicate method

inline string text_field(istream &in)

Inline functions are actual functions whose copy of the function body are injected directly into each place the function is called.

For details, please see the article

ld: duplicate symbol

3 Answers3

Linked