How do I use gcc, g++, and gdb?

The C compiler on eniac is gcc. Its C++ counterpart is g++.

To compile a C or C++ program:

% gcc file.c
or
% g++ file.c
This compiles file.c into an executable binary named a.out.

Here are a few options to gcc and g++:

-o outputfile
To specify the name of the output file. The executable will be named a.out unless you use this option.
-g
To compile with debugging flags, for use with gdb.
-L dir
To specify directories for the linker to search for the library files.
-l library
This specifies a library to link with.
-I dir
This specifies a directories for the compile to search for when looking for include files.

 


The debugger is gdb. Here is a typical example of a gcc/gdb session:
% cat hello.c
#include<stdio.h>

main() {
    int count;

    for (count=0;count<10;count++)
       printf("Hello from CETS!\n");
}
% gcc -g hello.c
% gdb ./a.out
GDB is free software and you are welcome to distribute copies of it
 under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.13 (sparc-sun-solaris2.3), 
Copyright 1994 Free Software Foundation, Inc...
(gdb) b main
Breakpoint 1 at 0x10784: file hello.c, line 6.
(gdb) r
Starting program: /home1/b/bozo/./a.out 


Breakpoint 1, main () at hello.c:6
6           for (count=0;count<10;count++)
(gdb) s
7              printf("Hello from CETS!\n");
(gdb) p count
$1 = 0
(gdb) disp count
1: count = 0
(gdb) set count=8
(gdb) s
Hello from CETS!
6           for (count=0;count<10;count++)
1: count = 8
(gdb) 
7              printf("Hello from CETS!\n");
1: count = 9
(gdb) c
Continuing.
Hello from CETS!

Program exited with code 01.
(gdb) q
%

Here are a few gdb commands:

help
Will give you help on most gdb functions. If you wish for help on a specific command, type help command.
b function-name
To set a breakpoint at a function.
r args
To run the program. It will run until it reaches a breakpoint.
s
To single-step through lines of code.
c
To continue until the next breakpoint.
p variable
To print a variable's value.
q
To quit gdb.

 

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