troubles in using GDB

**leiming** · 04-17-2008

Hi, there.
Today I use gdb to debug my homework but I meet troubles.
it's a program that get two arrays and then sort them and merge them then output them.
this is the trouble:

Code:

(gdb) b main
Breakpoint 1 at 0x4014af: file 9_14.c, line 43.
(gdb) r
Starting program: 1.exe

Breakpoint 1, main () at 9_14.c:43
43      int main(void){
(gdb) n
44              int const m = 5, n = 6;
(gdb) n
45              int a[m], b[n], c[m + n];
(gdb) n
46              get (a, m, b, n);
(gdb) p a
No symbol "a" in current context.
(gdb) n
47              sort(a, m);
(gdb) p a
No symbol "a" in current context.
(gdb)

how can I see the value in array a?
Thank you.

this is the source code:
(I have finished the debuging. but the question still exists)

Code:

#include <stdio.h>

void get(int a[], int m, int b[], int n){
	int i;
	for(i = 0; i < m; i++)
		scanf("&#37;d", &a[i]);
	for(i = 0; i < n; i++)
		scanf("%d", &b[i]);
}

void sort(int a[], int m){
	int i, j, t;
	for(i = 0; i < m; i++)
		for(j = m - 1; j > i; j--){
			if (a[j] < a[j - 1]){
				t = a[j];
				a[j] = a[j - 1];
				a[j - 1] = t;
			}
		}
}

void merge(int a[], int m, int b[], int n, int c[]){
	int ap = 0, bp = 0, cp = 0;
	while(ap < m && bp < n){
		if (a[ap] > b[bp])
			c[cp++] = b[bp++];
		else
			c[cp++] = a[ap++];
	}
	if(ap < m)
		memcpy(&c[cp], &a[ap], (m - 1 - ap) * sizeof(int));
	if(bp < m)
		memcpy(&c[cp], &a[bp], (n - 1 - bp) * sizeof(int));
}

void pr(int a[], int n){
	int i;
	for(i = 0; i < n; i++)
		printf("%d\t", a[i]);
}

int main(void){
	int const m = 5, n = 6;
	int a[m], b[n], c[m + n];
	get (a, m, b, n);
	sort(a, m);
	sort(b, n);
	merge(a, m, b, n, c);
	pr(c, m + n);
	return(0);
}

**tabstop** · 04-17-2008

When I run the same code, "p a" prints

Code:

$1 = (int (*)[0]) 0x22ff20

as befitting the fact that a is an array, and hence decays to a pointer when used by itself. Perhaps your compiler is complaining about the not-explicit array sizes? Edit: For completeness, I'm using gdb on MinGW.

**leiming** · 04-17-2008

Originally Posted by tabstop

When I run the same code, "p a" prints

Code:

$1 = (int (*)[0]) 0x22ff20

as befitting the fact that a is an array, and hence decays to a pointer when used by itself. Perhaps your compiler is complaining about the not-explicit array sizes? Edit: For completeness, I'm using gdb on MinGW.

yeah, If I can get that result, it is enough.
I use GDB on mingw, too.
I have another try, use "s" to go into a sub-function that array "a" is passed into, then I can see it. But in function "main" I still can't see it.
this is what I does:

Code:

(gdb) b main
Breakpoint 1 at 0x4014b6: file 9_14.c, line 43.
(gdb) r
Starting program: 1.exe

Breakpoint 1, main () at 9_14.c:43
43      int main(void){
(gdb) n
44              int const m = 5, n = 6;
(gdb) n
45              int a[m], b[n], c[m + n];
(gdb) n
46              get(a, m, b, n);
(gdb) n
47              sort(a, m);
(gdb) p a
No symbol "a" in current context.
(gdb) s
sort (a=0x22ff00, m=5) at 9_14.c:13
13              for(i = 0; i < m; i++)
(gdb) p a
$1 = (int *) 0x22ff00
(gdb) p *a@5
$2 = {3, 2, 1, 6, 5}
(gdb)

even though this is a way to see array "a", but in my opinion there is need for me to learn how to see a variable or array in any function.
I think GDB can offer it. If it can't, please tell me, then I'll give up.

**Elysia** · 04-18-2008

What platform? GDB is pesky command line, which makes it difficult to use IMHO.

**leiming** · 04-18-2008

Originally Posted by Elysia

What platform? GDB is pesky command line, which makes it difficult to use IMHO.

Windows XP.
More exactly, mingw, not cygwin.

Do you have any ideas?

**Elysia** · 04-18-2008

Visual Studio is your friend. All you'd have to do is hover your mouse over a variable to its contents.
I haven't used gdb, and I'm afraid I won't ever, so far as I'm concerned right now.

**leiming** · 04-18-2008

Originally Posted by Elysia

Visual Studio is your friend. All you'd have to do is hover your mouse over a variable to its contents.
I haven't used gdb, and I'm afraid I won't ever, so far as I'm concerned right now.

Thank you all the same.
In the past month I used VS 2005 Express but recently I want to try something new so I turn to GCC.

**Elysia** · 04-18-2008

Debugging using GDB is horrible, as you can see. I don't see why you don't stick to Visual studio instead.

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