Question

Here are my 2 source files:

main.c:

#include <stdio.h>
#include "part2.c"

extern int var1;
extern int array1[];

int main()
{
    var1 = 4;
    array1[0] = 2;
    array1[1] = 4;
    array1[2] = 5;
    array1[3] = 7;

    display();

    printf("---------------");

    printf("Var1: %d", var1);
    printf("array elements:");

    int x;
    for(x = 0;x < 4;++x)
        printf("%d: %d", x, array1[x]);

    return 0;
}

part2.c

#include <stdio.h>

int var1;
int array1[4];

void display(void);

void display(void)
{
    printf("Var1: %d", var1);
    printf("array elements:");

    int x;
    for(x = 0;x < 4;++x)
        printf("%d: %d", x, array1[x]);
}

When i try to compile the program this is what i get:

Ld /Users/John/Library/Developer/Xcode/DerivedData/Test-blxrdmnozbbrbwhcekmouessaprf/Build/Products/Debug/Test normal x86_64
cd /Users/John/Xcode/Test
setenv MACOSX_DEPLOYMENT_TARGET 10.7
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.7.sdk -L/Users/John/Library/Developer/Xcode/DerivedData/Test-blxrdmnozbbrbwhcekmouessaprf/Build/Products/Debug -F/Users/John/Library/Developer/Xcode/DerivedData/Test-blxrdmnozbbrbwhcekmouessaprf/Build/Products/Debug -filelist /Users/John/Library/Developer/Xcode/DerivedData/Test-blxrdmnozbbrbwhcekmouessaprf/Build/Intermediates/Test.build/Debug/Test.build/Objects-normal/x86_64/Test.LinkFileList -mmacosx-version-min=10.7 -o /Users/John/Library/Developer/Xcode/DerivedData/Test-blxrdmnozbbrbwhcekmouessaprf/Build/Products/Debug/Test

ld: duplicate symbol _display in /Users/John/Library/Developer/Xcode/DerivedData/Test-blxrdmnozbbrbwhcekmouessaprf/Build/Intermediates/Test.build/Debug/Test.build/Objects-normal/x86_64/part2.o and /Users/John/Library/Developer/Xcode/DerivedData/Test-blxrdmnozbbrbwhcekmouessaprf/Build/Intermediates/Test.build/Debug/Test.build/Objects-normal/x86_64/main.o for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I am using Xcode and both files are inside of a C project called Test

What is causing the error and how do i fix it?

Answer 1

Remove “#include "part2.c"” and change it to “#include "part2.h“

And move your function declaration of:

void display(void);

from the top of your “part.c” file into a file named “part2.h“, which should be included in (or put at the top of) both .c files.