zig creates a C library but not usable by C

Question

I'm able to get Zig to create a C library but when I attempt to use said library from a C program, it fails to find the definition of the included function.

My library definition:

const std = @import("std");

export fn removeAll(name: [*]const u8, len: u32) u32 {
    const n: []const u8 = name[0..len];
    std.fs.cwd().deleteTree(n) catch |err| {
        return 1;
    };
    return 0;
}

test "basic remove functionality" {
}

build.zig

const Builder = @import("std").build.Builder;

pub fn build(b: *Builder) void {
    const mode = b.standardReleaseOptions();
    const lib = b.addStaticLibrary("removeall", "src/main.zig");
    lib.setBuildMode(mode);
    switch (mode) {
        .Debug, .ReleaseSafe => lib.bundle_compiler_rt = true,
        .ReleaseFast, .ReleaseSmall => lib.disable_stack_probing = true,
    }
    lib.force_pic = true;
    lib.setOutputDir("build");
    lib.install();

    var main_tests = b.addTest("src/main.zig");
    main_tests.setBuildMode(mode);

    const test_step = b.step("test", "Run library tests");
    test_step.dependOn(&main_tests.step);
}

zig build creates the build directory with the libremoveall.a static library.

My C program:

#include <stdio.h>

int removeAll(char *, int);

int main(int argc, char **argv)
{
    removeAll("/tmp/mytest/abc", 15);
    return 0;
}

When I attempt to include it in my C program, it get the following error:

gcc -o main build/libremoveall.a main.c
/usr/bin/ld: /tmp/cckS27fw.o: in function 'main':
main.c:(.text+0x20): undefined reference to 'removeAll'

Any ideas on what I'm doing wrong? Thanks

EDIT

Thanks Paul R and stark, flipping the order worked. Can you help me understand why the order matter?

Try switching the order of main.c and the lib on your command line. — Paul R, Dec 07 '20 at 18:22
I also suggest objdump -ing the .a file to be sure the function is actually there as well. — Michael Dorgan, Dec 07 '20 at 18:24

score 6 · Accepted Answer · answered Dec 07 '20 at 21:30

The linker searches a library for unresolved references encountered so far in the process.

If you put your program after the library, there are no unresolved references when the linker reads the library. And then when it reads your program, there is no library to resolve the reference.

Swap your program and the library, and you are all set.

zig creates a C library but not usable by C

1 Answers1

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