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.

 

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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.