How to Print the Full Value of a Long String in Gdb

How do I print the full value of a long string in gdb?

set print elements 0

From the GDB manual:

set print elements number-of-elements

Set a limit on how many elements of an array GDB will print. If GDB is printing a large array, it stops printing after it has printed the number of elements set by the set print elements command. This limit also applies to the display of strings. When GDB starts, this limit is set to 200. Setting number-of-elements to zero means that the printing is unlimited.

Print whole string verbatim in gdb

set print repeats 0

Example:

(gdb) p "How to Print the Full Value of a Long String in GdbHow to Print the Full Value of a Long String in GdbHow to Print the Full Value of a Long String in Gdbaaaaaa"
$6 = 'a' <repeats 30 times>
(gdb) set print repeats 0
(gdb) p "How to Print the Full Value of a Long String in GdbHow to Print the Full Value of a Long String in GdbHow to Print the Full Value of a Long String in Gdbaaaaaa"
$7 = "How to Print the Full Value of a Long String in GdbHow to Print the Full Value of a Long String in GdbHow to Print the Full Value of a Long String in Gdbaaaaaa"
(gdb) set print repeats 10
(gdb) p "How to Print the Full Value of a Long String in GdbHow to Print the Full Value of a Long String in GdbHow to Print the Full Value of a Long String in Gdbaaaaaa"
$8 = 'a' <repeats 30 times>

GDB print all values in char array

You can use x/999bc, where 999 is the size of your array, for instance:

paul@thoth:~/src/sandbox$ gdb ./str
GNU gdb (GDB) 7.4.1-debian
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/paul/src/sandbox/str...done.
(gdb) list
1   int main(void) {
2       char * p = "hello\0world\0hahaha";
3       return 0;
4   }
5   
(gdb) b 3
Breakpoint 1 at 0x4004b8: file str.c, line 3.
(gdb) run
Starting program: /home/paul/src/sandbox/str 

Breakpoint 1, main () at str.c:3
3       return 0;
(gdb) print p
$1 = 0x40056c "hello"
(gdb) x/19bc p
0x40056c:   104 'h' 101 'e' 108 'l' 108 'l' 111 'o' 0 '\000'    119 'w' 111 'o'
0x400574:   114 'r' 108 'l' 100 'd' 0 '\000'    104 'h' 97 'a'  104 'h' 97 'a'
0x40057c:   104 'h' 97 'a'  0 '\000'
(gdb) 

Gdb printing long values in hex without having to guess the length

A way to display long (as well as ll & ull) values is with the g modifier. For example if we have a program which just stores

unsigned long long int a = 1234567891234567898;
int b = 23;
unsigned long long int c = 1111111111111111111;

by typing x/20xg $rsp (after the values have been moved to the stack) we get

0x7fffffffdd90: 0x0000000000000000    0x0000001755555040
0x7fffffffdda0: 0x112210f4c023b6da    0x0f6b75ab2bc471c7
0x7fffffffddb0: 0x0000000000000000    0x00007ffff7e08b25
...

With the long numbers in [rsp+0x10] & [rsp+0x18] being a & c respectively, and that 0x17 in [rsp+0xc] being b.

Print elements of C++ string vector nicely in GDB

Is there any way to view the elements nicely without displaying some part of the STL containers?

You either have a very old GDB, or some non-standard setup.

Here is what it looks like on a Fedora-34 system with default GDB installation:

(gdb) list
1       #include <string>
2       #include <vector>
3
4       int main()
5       {
6         std::vector<std::string> v;
7         v.push_back("abc");
8         v.push_back("abcdef");
9         v.push_back("ghi");
10      }
(gdb) b 9
Breakpoint 1 at 0x401378: file t.cc, line 9.
(gdb) run
Starting program: /tmp/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, main () at t.cc:9
9         v.push_back("ghi");
(gdb) p v
$1 = std::vector of length 2, capacity 2 = {"abc", "abcdef"}
(gdb) n
10      }
(gdb) p v
$2 = std::vector of length 3, capacity 4 = {"abc", "abcdef", "ghi"}
(gdb) q

How can I print the string value and not the hex in GDB debugger?

argv isn't a string, it's a char** - a pointer to the first of possibly multiple C strings.

I think you're looking for:

print argv[0]
print argv[1]
...

Or if you want to use printf:

printf "%s\n", argv[0]

But there's really no reason to in such a simple case, since gdb does know how to print char* strings.

Or, if you want to be fancy, this works:

print *argv@argc

The syntax FOO@NUM tells it to print an array of NUM elements starting at FOO. And I have no idea why the dereferencing works, but it does - I guess gdb is just nice like that. Someone enlighten me?

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