在用gdb调试程序的时候常常需要打印出string/char*类型的变量来看看结果，但是在调试Qt程序时因为QString的结构过于复杂，gdb默认无法打印出想要的东西，如下。

(gdb) print myString
$2 = {static null = {}, static shared_null = {ref = {atomic = 39},
    alloc = 0, size = 0, data = 0x82174ca, clean = 0, simpletext = 0, 
    righttoleft = 0, asciiCache = 0, reserved = 0, array = {0}}, 
    static shared_empty = {ref = {atomic = 1}, alloc = 0, size = 0, 
    data = 0xf5f71aca, clean = 0, simpletext = 0, righttoleft = 0,
    asciiCache = 0, reserved = 0, array = {0}}, d = 0x8260b48, 
    static codecForCStrings = 0x0}

为了使得qstring也能被正确打印出来，需要修改${HOME}/.gdbinit，在其中添加下面的一段脚本。

define printqs5
  set $d=$arg0.d
  printf "(Qt5 QString)0x%x length=%i: \"",&$arg0,$d->size
  set $i=0
  set $ca=(const ushort*)(((const char*)$d)+$d->offset)
  while $i < $d->size
    set $c=$ca[$i++]
    if $c < 32 || $c > 127
      printf "\\u%04x", $c
    else
      printf "%c" , (char)$c
    end
  end
  printf "\"\n"
end

Reference: A Printing routine for QString in GDB