These are also known as uninitialized memory reads (UMR) bugs. A classic case: local (or automatic) variables are, by definition, uninitialized (unlike globals, which are always preset to zero):
/* test case 1 : uninitialized var test case */static void uninit_var(){ int x; /* static mem */ if (x) printf("true case: x=%d\n", x); else printf("false case\n");}
In the preceding code, it's undefined what will occur at runtime as x is uninitialized and will thus have random content. Now, we run this test case as follows:
$ ./membugs 1true case: x=32604$ ./membugs 1true case: x=32611$ ./membugs 1true case: x=32627$ ./membugs 1true case: x=32709$
Thankfully, modern versions of the compiler (both gcc and ...
