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How to write a program to modify a word using a bit mask ?
#include <stdio.h> int main() { typedef int bool; bool f; /* conditional flag */ unsigned int m; /* the bit mask */ unsigned int w; /* the word to modify: if (f) w |= m; else w &= ~m; */ printf(“Enter the word to modify “); scanf(“%u”,&w); printf(“Enter the bit mask “); scanf(“%u”,&m); /* w […]
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Hacking the program for counting bits set
$gcc counting-bits-set-naive-way-related.c $./a.out Enter v 8474578 Total bits set in v is 11 $./a.out Enter v 1 Total bits set in v is 1 $./a.out Enter v 2 Total bits set in v is 1 $./a.out 3 Enter v a Total bits set in v is 0 $cat counting-bits-set-naive-way-related.c #include <stdio.h> int main() { unsigned […]
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How to find out if nth bit of a number is set to 1?
#include <stdio.h> int main() { int val1 = 4; int val2 = 18; int mask = 1; /* mask <<= 4; */ mask = mask << 4; printf(“mask is %d\n”,mask); if ( val1 & mask ) { printf(“Bit 5 in val1 is set\n”); } if (val2 & mask ) { printf(“Bit 5 in val2 is […]
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How to write a program to find if a number is a power of 2 ?
/* determining if an integer is a power of 2 */ #include <stdio.h> int main() { unsigned int v; /* we want to see if v is a power of 2 */ typedef int bool; bool f; printf(“enter number”); scanf(“%d”,&v); f = ( v & ( v – 1) ) == 0; printf(“the result is […]
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How to write a simple C program showing addition ?
$cat add-p1.c #include <stdio.h> #include <stdlib.h> int add (int a,int b) { return a + b; } int main() { int a,b; a =3; b =4; int ret = add(a,b); printf(“Result: %u\n”,ret); exit(0); } $gcc add-p1.c $./a.out Result: 7 $
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How to compile a program to use electric fence library for debugging ?
$cat efence-p1.c #include <stdio.h> #include <stdlib.h> int main() { char *ptr = (char *) malloc(1024); ptr[0] = 0; ptr[1024] = 0; exit(0); } $gcc -g efence-p1.c -lefence $./a.out Electric Fence 2.2 Copyright (C) 1987-1999 Bruce Perens <bruce@perens.com> Segmentation fault $
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Hacking with a program which has initialization of a MYSQL object
$ls connect1-p1.c $cp connect1-p1.c connect1-p2.c $emacs connect1-p2.c $gcc -lmysqlclient -g -L/usr/lib/mysql connect1-p2.c $./a.out mysql_init failed $echo $? 1 $./a.out 2> error.txt $cat error.txt mysql_init failed $emacs connect1-p2.c $gcc -lmysqlclient -g -L/usr/lib/mysql connect1-p2.c $./a.out mysql_init failed $./a.out 2> error.txt mysql_init failed $cat error.txt $
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