C++ linking object's files (G++)

Question

class.h

#include <iostream>
#include <stdint.h>

using namespace std;

template <typename T>
class CIntegerType {
 public:
    void Show ( void );

 private:
    T m_Data;
};

class.cpp

#include "class.h"

template <typename T>
void CIntegerType<T> :: Show ( void ) {
    cout << m_Data << endl;
}

main.cpp

#include "class.h"

int main ( void ) {
    CIntegerType<uint32_t> UINT32;

    UINT32 . Show ();

    return 0;
}

This commands return:

g++ -Wall -pedantic -c main.cpp

g++ -Wall -pedantic -c class.cpp

g++ -Wall -pedantic -o class.o main.o

main.o: In function `main': main.cpp:(.text+0x11): undefined reference to 'CIntegerType< unsigned int>::Show()' collect2: ld returned 1 exit status

g++ -Wall -pedantic **-o class.o** main.o -- Looks like you're missing an argument — Steven Maitlall, May 28 '13 at 20:37
You might need to switch the objects around, My memory fails me but I think you must always specify your main loop object first when compiling. — Syntactic Fructose, May 28 '13 at 20:42
Try putting the template function in the header. See: http://stackoverflow.com/questions/495021/why-can-templates-only-be-implemented-in-the-header-file — shawn, May 28 '13 at 21:37

score 1 · Answer 1 · edited May 23 '17 at 11:45

1

Try g++ -Wall -pedantic -o main.o class.o instead. You are facing the same problem as in this question: g++ linking order dependency when linking c code to c++ code

The linker searches for functions in the order they appear. Since you have a template function, its use in main must be fed to the linker prior to the actual code to instantiate it in class.

edited May 23 '17 at 11:45

Community

1
1

answered May 28 '13 at 20:42

Marc Claesen

16,778
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Thanks. I tried it. Output: /usr/bin/ld: /usr/lib/debug/usr/lib/i386-linux-gnu/crt1.o(.debug_info): relocation 0 has invalid symbol index 12 ... : In function `_start': (.text+0x18): undefined reference to `main' collect2: ld returned 1 exit status – Peter K. May 28 '13 at 20:45
I tried both variant "g++ -Wall -pedantic -o main.o class.o" and "g++ -Wall -pedantic -o class.o main.o", but no result. – Peter K. May 28 '13 at 20:50

score 1 · Accepted Answer · edited May 23 '17 at 12:13

1

Try putting your template implementation in the header file.

See: Why can templates only be implemented in the header file?

edited May 23 '17 at 12:13

Community

1
1

answered May 28 '13 at 21:38

shawn

336
1
3

C++ linking object's files (G++)

2 Answers2

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