I want to make a static library for other programs to use, but I don't know why it failed-CodePudding

This is the source code of the file:

fileselector.h:

#ifndef FILE_SELECTOR
#define FILE_SELECTOR

const char *open_file_dialog();

const char *save_file_dialog();

#endif

linux/fileselector.cpp:

#include <cstring>
#include "../fileselector.h"
#include <iostream>

const char *open_file_dialog() {
    ...
}

const char *save_file_dialog() {
    ...
}

This is my static library production steps:

$ gcc linux/fileselector.cpp fileselector.h -c
$ ar rs libfileselector.a fileselector.o

This is a test using a static library:

main.c

#include "fileselector.h"

int main() {
    open_file_dialog();
    return 0;
}

$ gcc main.c -L. -lfileselector -o main
/usr/bin/ld: /tmp/ccOTrMR8.o: in function `main':
main.c:(.text 0xa): undefined reference to `open_file_dialog'
collect2: error：ld return 1

Where is the problem?

CodePudding user response：

You defined a set of C functions but are using them from a C program.

Function names in C are mangled during the compilation phase to allow for multiple functions with the same name but different signatures to exist. C programs don't do name mangling, so the compiled name of the library functions don't match the plain function name that the C program expects.

If you want C functions to be usable by a C program, you need to disable name mangling by adding extern "C" around the definitions and declarations.

So your C source file would look like this:

extern "C" {

const char *open_file_dialog() {
    ...
}

const char *save_file_dialog() {
    ...
}

}

And your header would look like this:

#ifdef __cplusplus
extern "C" {
#endif

const char *open_file_dialog();

const char *save_file_dialog();

#ifdef __cplusplus
}
#endif

The #ifdef's in the header are needed because extern "C" is a C only feature.

Also, it's not necessary to list the header file when compiling. Because it is included in the source file it is already being compiled.