Debugging with gdb
==================

Our Demo Code:

    #include <stdio.h>
    #include <stdint.h>

    int g_myvar = 42;
    #define MYCONST 99

    void sideeffect(void){
        g_myvar += MYCONST;
    }

    uint8_t myfunction(uint8_t x){
        return x+42;
    }

    int main(void){

        uint8_t foo = 23;
        uint8_t bla = 23;

        uint8_t x = foo + bla;
        uint8_t i;

        uint8_t y = myfunction(bla);

        uint8_t * verybad = 0;
        
        printf("%d\n", foo);
        printf("%d\n", y);
        // use this printf to cause a segfault
        // printf("%d\n", *verybad);

        for(i = 0; i < 10; ++i){
            y = myfunction(y);
            sideeffect();
        }
        printf("%d\n", y);


        return 0;
    }

Resources
---------

* Vorlesungsfolien Betriebssysteme UE auf der TU Wien:
[Debugging](http://ti.tuwien.ac.at/cps/teaching/courses/osue/slides/ss14_entwicklung_in_c.pdf)
* Online Tutorial auf [beej.us](http://beej.us/guide/bggdb/)

Basics
------

* gcc -g test.c -o test
* gdb test
* gdb test core
* gdb --args

Commands in GDB
---------------

* break
* continue
* next
* info breakpoints
* watch
* list
* print
* bt full
* catch signal
* run
* break .. if ...
* delete
* disable
* enable
* step
* stepi
* target record-full
* reverse-next
* set
* quit

Show preprocessor macros
------------------------

See [Thread on
SO](http://stackoverflow.com/questions/2934006/how-do-i-print-a-defined-constant-in-gdb)

    gcc -g3 test.c
    gdb a.out
    (gdb) info macro MYCONST
    (gdb) macro expand MYCONST

Fun with print
--------------

* print myfunction(y+23/7)/23.0
* print printf("%d\n", 23 > 42 ? 111 : 222) 


Enable history
--------------

create a file .gdbinit in ~ and put this line in:

    set history save on