CODEWITHSUNDEEP
scriptingwhile-loopgdb
Tem Pora
Tem Pora

Reputation: 2093

gdb command files error "Invalid type combination" in while loop

I wrote following commands in my gdb command file.

while ($i < 3)
s
end

I got the error: Invalid type combination in ordering comparison.

Then I tried, the following:

while (((int) $i) < ((int) 3))
s
end

But then I got the error: Invalid cast.

How to write a loop in gdb command file?

Note: i is the variable in my C program being debugged that is referred as $i in the command file.

I couldn't find any examples at this site, which gives some reference material on gdb.

Upvotes: 2

Views: 2187

Answers (1)

user184968
user184968

Reputation:

First, I think it is more appropriate to use 

watch  i >= 3

In order to break when i becomes more than 2.

As for looping until a local varible in C is less than 3. This is a gdb script for it:

  while (i < 3) 
    s
  end

This in C++ code to demonstrate a gdb loop:

#include <stdio.h>

int main()
{
  for (int i=0; i< 10; ++i) {
    printf ("i: %d\n", i);
  }
  return 0;
}

This is a gdb test:

D:\>gdb -q a
Reading symbols from D:\a.exe...done.
(gdb) start
Temporary breakpoint 1 at 0x401395: file main.cpp, line 4.
Starting program: D:\a.exe
[New Thread 3780.0x144]

Temporary breakpoint 1, main () at main.cpp:4
4       {
(gdb) n
5         for (int i=0; i< 10; ++i) {
(gdb)
6           printf ("i: %d\n", i);
(gdb) while (i<3)
 >s
 >end
i: 0
5         for (int i=0; i< 10; ++i) {
6           printf ("i: %d\n", i);
i: 1
5         for (int i=0; i< 10; ++i) {
6           printf ("i: %d\n", i);
i: 2
5         for (int i=0; i< 10; ++i) {
6           printf ("i: %d\n", i);
(gdb) p i
$1 = 3
(gdb)

Upvotes: 1

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