C programming: How to use gdb with Makefile and command line arguments?

Question

To create the .out executable, I have to enter: ``` $: make $: myprogram.out name.ged ``` My program incorporates a command line argument, thus the "name.ged". Whenever I run gdb after getting a segmentation fault (core dumped), I enter: ``` $: gdb a.out core (gdb): bt ``` I then use the back trace command, and gdb returns: ``` #0 0x4a145155 in ?? () #1 0x08a16ce0 in ?? () ``` I even tried using the up command t move up the stack, but still no luck. I can't tell which line in my program is giving me the seg fault. gdb works with my other programs that do not involve a Makefile and command arguments, so I'm wondering if my commands are incorrect.

Accepted Answer

Summarizing the comments (before anyone else does :).

Your executable file is missing the symbolic information that gdb needs to display the relevant source code. You need to add the `-g` option to the compile command and produce a new executable. Then re-run your failing test to produce a new core file. gdb with this executable and core will be able to show you the stack of function calls using `backtrace`.

In a makefile, the easiest way to do this is to add (to) the `CFLAGS` variable which is used with the implicit .o.c rule.

```
CFLAGS= -g -Wall -Wextra
```

You can also add this directly to the command-line (assuming a decent shell :). This sets the value as an environment variable during the execution of the `make` command (and sub-commands).

```
$ CFLAGS='-g -Wall -Wextra' make
```

I'd actually recommend you add this to your bash .profile, so you always get the most information from the compiler.

```
CFLAGS='-Wall -Wextra'
```

Then, when you need it, put this in the makefile to make a debuggable executable:

```
CFLAGS+= -g
```

C programming: How to use gdb with Makefile and command line arguments?

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