Undefined reference to 'function' yet the header is included

Question

I am playing around with the ci20 and flowcloud. I have downloaded their c library/sdk and have included the header.

The program is simply:

#include <stdio.h>
#include <stdbool.h>
#include <flow/flowcore.h>

int main (int argc, char*argv[])
{
    printf("hello");
    if(FlowCore_Initialise()) printf("init");
    return (0);
}

but on compilation gcc -Wall test.c -o hello I get this error:

/tmp/cch4kocL.o: In function `main':
test.c:(.text+0x40): undefined reference to `FlowCore_Initialise'
collect2: error: ld returned 1 exit status

I am not 100% sure what is going on here.

It's a **linker** error and not a **compilation** error, you don't link with the flowcloud library. — Jabberwocky, Feb 10 '16 at 11:13
You probably need something as 'gcc -Wall **-lflow\flow.a** test.c -o hello', where **flow.a** is your library (not sure about the flow.a filename, look in the flow directory and/or read the documentation of the flow library. — Jabberwocky, Feb 10 '16 at 11:31
@MichaelWalz: The library needs to be specified *after* the object needing it. — alk, Feb 10 '16 at 16:21
@alk, right, I'm not used to Linux, therefore I wrote "something as". But apparently the OP understood what to do. — Jabberwocky, Feb 10 '16 at 16:31

score 2 · Accepted Answer · answered Feb 10 '16 at 11:49

You are getting a linker error. When compiling with gcc, you need to also specifiy the library you want to link to in addition to just using the proper #include 's.

The syntax for compiling with gcc is

$ gcc [options] [source files] [object files] [-Ldir] -llibname [-o outfile]

As you can see you can link the library by adding -l<name> to your command string.

Undefined reference to 'function' yet the header is included

1 Answers1