El 11/04/2010 8:37, Jesus Sanchez escribis:
i don't think so. Use gdb and see where you are writing to. Based on your description of your a.c and b.c, I assume in a.c you have "char foo;" (global), and in b.c you by mistake have "extern int foo;". If your foo variable is at address, say 0x11111111, and you write two bytes to that address, where foo is in fact a char (single byte), the other byte will be written to address 0x11111112. You can test this with a simple example program, where you can declare other char variables around your foo variable and print all of them after the foo assignment and see which ones got clobbered. Then again, maybe I'm misunderstanding your initial problem, you didn't show your code. --patrick Breakpoint 1, main (argc=1, argv=0xfffc8c8c) at a.c:30 30 bar(); (gdb) p&f $1 = (int *) 0x1842116 (gdb) x/4b 0x1842116 0x1842116<f>: 0x00 0x00 0x00 0x00 bar () at b.c:14 14 f = 0x44332211; (gdb) n 16 } (gdb) x/4b 0x1842116 0x1842116<f>: 0x44 0x33 0x22 0x11 (gdb) p&g $2 = 0x1842117 "3\"\021" (gdb) p&k $3 = 0x1842119 "\021" (gdb) p&l $4 = 0x1842118 "\"\021" (gdb) p/x f $13 = 0x44332211 (gdb) p/x g $14 = 0x33 (gdb) p/x l $15 = 0x22 (gdb) p/x k $16 = 0x11 Looks like the "extern int foo;" confused gdb.I'm not using extern for the variables, anyway here is the code (to a extremely basic level) using your hint about making more char variables around foo to show them later: all compiled with gcc -Wall -W without warning ---------- a.c ------------------------------------------ #include <stdio.h> char foo; char foo1; char foo2; char foo3; void overfoo(); /* the func that will overflow the foo variable */ int main(){ overfoo(); /* after calling we have 0x2211 on foo variable */ printf("%x\n",foo); printf("%x\n",foo1); printf("%x\n",foo2); printf("%x\n",foo3); return 0; } ---------- b.c ------------------------------------------ int foo; /* here the problem begins */ void overfoo(){ foo=0x2211; } --------------------------------------------------------------- after compiling and executing , foo showed 0x11 and other 0x0. thanks for your time. -J
