gcc - undefined reference to `libusb_init'

Question

I'm trying to compile a piece of code which uses libusb:

#include <stdio.h>
#include <libusb-1.0/libusb.h>
#include <assert.h>

int main(void) {
    libusb_context *context = NULL;
    int rc = 0;

    rc = libusb_init(&context);
    assert(rc == 0);

    libusb_exit(context);
    return 0;
}

Upon compiling with gcc -lusb -lusb-1.0 sample.c -o sample the following errors emerge:

/tmp/ccr65JBT.o: In function `main':
sample.c:(.text+0x2e): undefined reference to `libusb_init'
sample.c:(.text+0x62): undefined reference to `libusb_exit'
collect2: error: ld returned 1 exit status

To make sure libusb is availible on my system:

raven@enforcer:~/sample$ pkg-config --libs libusb-1.0
-lusb-1.0
raven@enforcer:~/sample$ pkg-config --libs libusb
-lusb

I'm running Ubuntu 18.04 with gcc 7.3.0-16ubuntu3, how to fix?

Possible duplicate of [Why does the order in which libraries are linked sometimes cause errors in GCC?](https://stackoverflow.com/questions/45135/why-does-the-order-in-which-libraries-are-linked-sometimes-cause-errors-in-gcc) — Ctx, Jul 02 '18 at 11:45
I have an answer to a similar question: https://stackoverflow.com/a/74634657/5432351 — gojimmypi, Nov 30 '22 at 22:05

score 5 · Accepted Answer · answered Jul 02 '18 at 11:06

5

Got it working by appending the flags after the .c: gcc sample.c -o sample -lusb -lusb-1.0

Autotools: sample_LDADD instead of sample_LDFLAGS

Thanks to Felix Palmen.

answered Jul 02 '18 at 11:06

Henk Schurink

419
6
17

1

rough explanation: a linker typically works by holding a list of unresolved symbols and looking to resolve them from the object files (or archives or libraries) it encounters later ... and GCC lets the linker process the object files in the order they appear on the initial command line. – Jul 02 '18 at 11:23

gcc - undefined reference to `libusb_init'

1 Answers1