Re: finding sizeof structure using gdb

On Jan 28, 2:54 pm, fnegroni <f.e.negr...@xxxxxxxxxxxxxx> wrote:
I think the command you are looking for is:
print _expr_
where _expr_ is the expression you want to evaluate at runtime.
You can place a breakpoint anywhere in your program where you want to
evaluate an expression, and type 'print' followed by the expression
such as 'sizeof (struct_type)'
To find out the offset of a member it necessitates some casts:

Say you have a struct defined as:

struct kelp_file {
FILE *f;
char *name;

};

and at some point an object of type struct kelp_file called k comes
into visibility.

Use gdb to print offset of name compared to start of structure:

print (size_t)&(k.name) - (size_t)(&k)

Thanks Guys, that was really helpful.
Can you please also tell me how to typecast a memory address to a
particular structure type and print the values of various membes of
that structure.
For eg. Say I have some "structure x" at address 0xffff1000
Now, I want to typecast this memory address 0xffff1000 with the
"structure x" and print the contents of all the members in "structure
x". Can it be done in GDB Or I have to dump the contents of memory and
manually interpret the value of each member ?
.

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