Question

When I use set logging on in gdb, the output to the log file has a different format than what I see on the terminal screen. The logfile is not very readable. How can I get the log file in a readable format?

Output to screen is fine:

(gdb) p foo
$1 = {
  static npos = 18446744073709551615,
  _M_dataplus = {
    <std::allocator<char>> = {
      <__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>},
    members of std::basic_string<char,std::char_traits<char>,std::allocator<char> >::_Alloc_hider:
    _M_p = 0x601028 "Hello World!\n"
  }
}

Output to log file is not very readable:

^Z^Zpost-prompt

^Z^Zbreakpoints-headers

^Z^Zfield 0
Num     
^Z^Zfield 1
Type           
^Z^Zfield 2
Disp 
^Z^Zfield 3
Enb 
^Z^Zfield 4
Address            
^Z^Zfield 5
What

^Z^Zbreakpoints-table

^Z^Zrecord

^Z^Zfield 0
1       
^Z^Zfield 1
breakpoint     
^Z^Zfield 2
keep 
^Z^Zfield 3
y   
^Z^Zfield 4
0x0000000000400961 
^Z^Zfield 5
in main at test.cpp:9
        breakpoint already hit 1 time

^Z^Zbreakpoints-table-end

^Z^Zpost-prompt

^Z^Zvalue-history-begin 1 -
$1 = 
^Z^Zvalue-history-value
{

^Z^Zfield-begin -
static npos
^Z^Zfield-name-end
 = 
^Z^Zfield-value
18446744073709551615
^Z^Zfield-end
, 

^Z^Zfield-begin -
_M_dataplus
^Z^Zfield-name-end
 = 
^Z^Zfield-value
{
    <std::allocator<char>> = {
      <__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
    members of std::basic_string<char,std::char_traits<char>,std::allocator<char> >::_Alloc_hider: 

^Z^Zfield-begin *
_M_p
^Z^Zfield-name-end
 = 
^Z^Zfield-value
0x601028 "Hello World!\n"
^Z^Zfield-end

  }
^Z^Zfield-end

}

^Z^Zvalue-history-end

^Z^Zpost-prompt

^Z^Zbreakpoints-headers

^Z^Zfield 0
Num     
^Z^Zfield 1
Type           
^Z^Zfield 2
Disp 
^Z^Zfield 3
Enb 
^Z^Zfield 4
Address            
^Z^Zfield 5
What

^Z^Zbreakpoints-table

^Z^Zrecord

^Z^Zfield 0
1       
^Z^Zfield 1
breakpoint     
^Z^Zfield 2
keep 
^Z^Zfield 3
y   
^Z^Zfield 4
0x0000000000400961 
^Z^Zfield 5
in main at test.cpp:9
        breakpoint already hit 1 time

^Z^Zbreakpoints-table-end

^Z^Zpost-prompt

Answer 1

You must be using this from some kind of IDE, which turns on MI (machine interface). The output you see is made for easy parsing by another program, but not for human consumption.

It is likely a bug that MI interface also affects the format of gdb.txt log. Please file a bug about it here.

As a workaround, run GDB outside of the IDE to collect easy to read gdb.txt.