This is the example program we'll be using to demonstrate how you would typically use gdb to track down bugs. It has a number of bugs, some obvious, some not so obvious. It compiles with no warnings using 'gcc -g ecount1.c -o ecount1'
The program has a simple task to perform - it takes one parameter, a single word, and counts the number of letter 'e's in it. It prints the result to the screen. That shouldn't be too difficult, should it?
/*
* ecount1.c Simple program to count the number of letter 'e's that
* appear in the word given as the only parameter
*
* WARNING: This program contains several deliberate bugs
* (and possibly some others...)
*/
#include <stdio.h>
int main( int argc, char *argv[] )
{
char *buf=NULL;
int count, i;
/* check we have a parameter */
if( argc = 1 )
{
printf( "Usage: ecount <word>\n");
exit(1);
}
/* Make our own local copy of argv[1] */
strcpy( buf, argv[1] );
/* print it out to show we received it correctly
printf( "The word is '%s'\n", buf );
/* Now step through counting letter 'e's */
for( i=0; i<strlen(buf); ++i )
{
if( buf[i] == 'e' ) ++count;
}
return(0);
}