c - difficulties with bit operations

Question

I'm debugging a program with GDB.

unsigned int example = ~0;

gives me:

(gdb) x/4bt example
0xffd99788:     10101000        10010111        11011001        11111111

why is this not all 1's? i defined it as ~0... then the next line of code is:

example>>=(31);

and GDB gives me this when I try to examine the memory at bits:

(gdb) x/4bt example
0xffffffff:     Cannot access memory at address 0xffffffff

what is going on???

Answer 1

You need to take the address of example in the gdb statement:

(gdb) x/4bt &example

Answer 2

I think that the x command examines memory, so example would be interpreted as pointer. Try

x/4bt &example

or simply

print /x example

Answer 3

I haven't checked the gdb command format but looking at the last statement it seems like you want to see what is at the address stored in example instead of printing example ... it seems that example is all 1s (0xffffffff) and you are trying to look at that location in memory when you get the error.