Compiling C code using zmq API

Question

I am failed to compile builtin example hwserver.c using ZeroMQ APIs. I have tried every possible way.

gcc -lzmq hwserver.c -o hwserver

It prompts me with:

 hwclient.c:(.text+0x22): undefined reference to `zmq_ctx_new'
 hwclient.c:(.text+0x3a): undefined reference to `zmq_socket'
 hwclient.c:(.text+0x52): undefined reference to `zmq_connect'
 hwclient.c:(.text+0x94): undefined reference to `zmq_send'
 hwclient.c:(.text+0xb8): undefined reference to `zmq_recv'
 hwclient.c:(.text+0xe4): undefined reference to `zmq_close'
 hwclient.c:(.text+0xf0): undefined reference to `zmq_ctx_destroy'
 collect2: error: ld returned 1 exit status

I'm using zeromq-3.2.2 on ubuntu-12.10

Any help really appreciated.

Thanks,

-Sam

Answer 1

Order of arguments to gcc does matter a lot.

Try

 gcc -Wall -g hwserver.c -lzmq -o hwserver

You need first the warning and optimizations or debugging flags (e.g. -Wall for all warnings, -g for debugging information), then the optional preprocessor flags (like -D or -I but you have none of them), then the source files, and at last the libraries -lzmq (order is relevant: from high level libraries to low level ones) and the output option -o hwserver (which could be elsewhere).

Read the gcc documentation, notably the chapter about invoking GCC.

Don't forget the -Wall : you really want to get all warnings, and you should improve your code till no warnings are given. You could even want -Wextra to get more extra warnings.

Don't forget the debugging information flag -g: you will need to use the gdb debugger to debug your program.

Later, use -O or -O2 to optimize the binary program (the compiler will then produce more efficient, but less debuggable, machine code). Care about that only when your program is debugged.

As soon as you want to develop real-sized C programs (i.e. your project made of several source files and some header file[s]), you'll need a builder infrastructure, like GNU make (a very common builder; you could try omake instead).

See also this answer to a related question.