将程序与两个静态库链接在一起，每个静态库都包含依赖于另一个函数的函数？

Question

I'm actually trying to call a function a (stocked in liba.a) from another function b (stocked in libb.a) but I have a linkage error.

There are my files:

ac

#include <stdio.h>
void a()
{
  printf("a\n");
}

bc

void a();
void b()
{
  a();
}

main.c

void b();
int main(int argc, char const* argv[])
{
  b();
  return (0);
}

And how I compiled

gcc -c a.c
gcc -c b.c
ar rc liba.a a.o
ar rc libb.a b.o
ranlib liba.a
ranlib libb.a
gcc main.c liba.a libb.a

(the exact message error)

b.c:(.text+0xa): undefined reference to `a'

Is there a way to do what I'm trying to do? Thanks for your time

EDIT: It appears that library order in the command line matters. But in my real problem libA depends on libB and libB depends on libA (which the MCVE code doesn't demonstrate).

Answer 1

EDIT: It appears that library order in the command line matters. But in my real problem libA depends on libB and libB depends on libA (which the MCVE code doesn't demonstrate).

Your real problem, then, is you've painted yourself in a corner. The right thing to do is arrange the two libraries so that one is entirely independent of the other, and put that one after the other in the link command.

Without making that change, you might get away with mentioning the first library twice,

gcc main.c liba.a libb.a liba.a

The linker is pretty simple-minded when it comes to name resolution. Starting with a list of unresolved names, it marches through the list of libraries, resolving names as it finds them. It won't notice that you give it liba.a twice; it will resolve the a names supplied by b , and then the b names supplied by a .

But that trick is likely to bite you one day (if it works at all). Best, as I said, is to sort out your dependencies and simplify things for yourself and those who follow you.

Answer 2

Create the following Makefile in the same directory that you already have ac , bc and main.c :

#!/usr/bin/make

ar:
        gcc -o a.o -c a.c
        gcc -o b.o -c b.c
        gcc -o m.o -c main.c
        ar rc liba.a a.o
        ar rc libb.a b.o
        ar rc libm.a m.o
        ranlib liba.a
        ranlib libb.a
        ranlib libm.a
        gcc -o main m.o a.o b.o

install:
        gcc -o a.o -c a.c
        gcc -o b.o -c b.c
        gcc -o m.o -c main.c
        gcc -o main m.o a.o b.o

clean:
        rm -f *.o
        rm -f *.a
        rm -f main

Basically, your question is an example of multiple files development in C.

• If you issue the make install command, the Makefile will compile your program using standard gcc compilation process.
• If you issue the make ar , the compilation will be ar packaging compliance.
• If you issue the make clean , the Makefile will clean your previous build