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问题背景：

GDB调试C程序时，经常需要打印结构体的内容，默认情况下输出很不直观，看起来很费劲，比如：

(gdb) p *ht
$6 = {gc = {refcount = 1, u = {v = {type = 7 '\a', flags = 0 '\000', gc_info = 0}, type_info = 7}}, u = {v = {flags = 18 '\022', nApplyCount = 0 '\000', 
      nIteratorsCount = 0 '\000', reserve = 0 '\000'}, flags = 18}, nTableMask = 4294967294, arData = 0x845cd5c, nNumUsed = 0, nNumOfElements = 0, nTableSize = 8, 
  nInternalPointer = 4294967295, nNextFreeElement = 0, pDestructor = 0x82581ff <_zval_ptr_dtor_wrapper>}

解决方案：

GDB对此早有考虑，所以给我们提供了很多可配置的选项，对于结构体，只需打开如下配置即可：(gdb) set print pretty on

效果展示：

(gdb) 
$9 = {
  gc = {
    refcount = 1, 
    u = {
      v = {
        type = 7 '\a', 
        flags = 0 '\000', 
        gc_info = 0
      }, 
      type_info = 7
    }
  }, 
  u = {
    v = {
      flags = 18 '\022', 
      nApplyCount = 0 '\000', 
      nIteratorsCount = 0 '\000', 
      reserve = 0 '\000'
    }, 
    flags = 18
  }, 
  nTableMask = 4294967294, 
  arData = 0x845cd5c, 
  nNumUsed = 0, 
  nNumOfElements = 0, 
  nTableSize = 8, 
  nInternalPointer = 4294967295, 
  nNextFreeElement = 0, 
  pDestructor = 0x82581ff <_zval_ptr_dtor_wrapper>
}

扩展知识：

除了结构体外，GDB还针对联合体、数组等实体提供了类似的配置指令，格式均为：

//查看某个实体的当前配置
show print 实体

//打开或关闭某个实体配置
set  print 实体 [on|off]

//比如查看数组以及打开或关闭数组开关
show print array
set  print array on
set  print array off