gdb:显示某些数据的typeinfo

Question

基本上,我想得到typeid(*this).name(),即真正的类型this.

我想在GDB中得到它(不修改源代码).我尝试过,print typeid(*this)但它说typeid未知(因为我没有把它包含在源文件中).

Answer 1

使用ptype命令,如下所示:

(gdb) ptype 42
type = int

Answer 2

使用ptype、whatis、 和explore（我最喜欢的！）：

其中您有一个名为的变量value，其定义为：

uint32_t value = 1234;

...以下所有工作：

1. ptype value节目unsigned int
2. whatis value节目uint32_t
3. explore value（我最喜欢的！）显示：

   The value of 'value' is of type 'uint32_t' which is a typedef of type 'unsigned int'
   'value' is a scalar value of type 'unsigned int'.
   value = 1234
   

例子：

The value of 'value' is of type 'uint32_t' which is a typedef of type 'unsigned int'
'value' is a scalar value of type 'unsigned int'.
value = 1234

感谢@o11c 下面的评论指出了该whatis命令的存在。

我explore通过在 gdb 中运行发现了该命令help all。请参阅下面“参考文献”部分中我的评论。

自己尝试一下：

(gdb) ptype value
type = unsigned int
(gdb) ptype &value
type = unsigned int *
(gdb) whatis value
type = uint32_t
(gdb) explore value
The value of 'value' is of type 'uint32_t' which is a typedef of type 'unsigned int'
'value' is a scalar value of type 'unsigned int'.
value = 1234

现在，在gdb运行时执行以下操作：

# download the file "type_punning.c"
wget https://raw.githubusercontent.com/Generalsimus/eRCaGuy_hello_world/master/c/type_punning.c

# build it with optimization OFF (`-O0`) and debugging symbols ON (`-ggdb`), 
# and output all intermediary files (`-save-temps=obj`), and run it in the 
# gdb debugger (`gdb bin/type_punning`)
mkdir -p bin && gcc -Wall -Wextra -Werror -O0 -ggdb -std=c11 -save-temps=obj \
type_punning.c -o bin/type_punning && gdb bin/type_punning

完整示例命令和输出：

eRCaGuy_hello_world/c$ mkdir -p bin && gcc -Wall -Wextra -Werror -O0 -ggdb -std=c11 -save-temps=obj type_punning.c -o bin/type_punning && gdb bin/type_punning
GNU gdb (Ubuntu 8.1.1-0ubuntu1) 8.1.1
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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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".
Type "show configuration" for configuration details.
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<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from bin/type_punning...done.
(gdb) b type_punning.c:52
Breakpoint 1 at 0x70b: file type_punning.c, line 52.
(gdb) r
Starting program: /home/gabriel/GS/dev/eRCaGuy_hello_world/c/bin/type_punning 
Type punning and ptr-based serialization demo
TECHNIQUE 1: union-based type punning:

Breakpoint 1, main () at type_punning.c:53
53          printf("1st byte = 0x%02X\n", (u.bytes)[0]);
(gdb) ptype u.value
type = unsigned int
(gdb) whatis u.value 
type = uint32_t
(gdb) explore u.value  
The value of 'u.value' is of type 'uint32_t' which is a typedef of type 'unsigned int'
'u.value' is a scalar value of type 'unsigned int'.
u.value = 1234
(gdb) 

我的旧/原始答案

正如@Star Brilliant 在这里所说的那样：

ptype my_var

返回类似 的东西type = unsigned short，但我希望它返回type = uint16_t，这样我在检查内存时可以真正知道它有多少字节。我能想到的要获得这种效果的最好方法是：

print &my_var

它打印(uint16_t *) 0x7ffffffefc2c，从而揭示它的指针类型是uint16_t*，这意味着它的类型是uint16_t。

我发现这比 更有用ptype my_var，但是如果您有任何建议，则需要一种更直接的方法来获得此效果。

gdb 命令和输出示例：

(gdb) ptype my_var
type = unsigned short
(gdb) print &my_var
$27 = (uint16_t *) 0x7ffffffefc2c

同样，通知ptype my_var揭示了它是一个unsigned short，而print &my_var揭示了更详细和期望的答案，即它是一个uint16_t。

参考：

1. @o11c 的评论如下
2. @星耀的回答
3. help all- 我在运行时使用了此命令gdb，将输出全部复制粘贴到文本编辑器，然后搜索“type”以发现该explore命令。

也可以看看：

1. 我对如何在 GDB 中查看像数组一样的指针？
2. 我对如何printf在 GDB 中使用以便围绕变量输出编写自定义描述的回答
3. [我的回答] “gdb”调试器奇怪地跳过断点
4. [我的问答]编译器的“-O0”选项和“-Og”选项有什么区别？
5. [我的问答] https://askubuntu.com/questions/1349047/where-do-i-find-core-dump-files-and-how-do-i-view-and-analyze-the-backtrace-st

_{关键词：如何运行gdb；如何在gdb中查看变量类型和值；如何构建和编译 gdb 调试符号}

Answer 3

'ptype [ARG]'命令将打印该类型.

Answer 4

这个问题可能是相关的:使用gdb的C++多态类中的vtable:

(gdb) help set print object
Set printing of object's derived type based on vtable info. 

它不完全是typeid(),但它应该在检查多态指针时显示真实的对象类型(例如this在基类中).当然只适用于具有vtable的类(即至少一个虚拟方法),但也适用typeid.