# 使用“$_exitcode”變量 ## 例子 int main(void) { return 0; } ## 技巧 當被調試的程序正常退出時，gdb會使用`$_exitcode`這個“`convenience variable`”記錄程序退出時的“`exit code`”。以調試上面程序為例: [root@localhost nan]# gdb -q a Reading symbols from a...done. (gdb) start Temporary breakpoint 1 at 0x400478: file a.c, line 3. Starting program: /home/nan/a Temporary breakpoint 1, main () at a.c:3 3 return 0; (gdb) n 4 } (gdb) 0x00000034e421ed1d in __libc_start_main () from /lib64/libc.so.6 (gdb) Single stepping until exit from function __libc_start_main, which has no line number information. [Inferior 1 (process 1185) exited normally] (gdb) p $_exitcode $1 = 0 可以看到打印的`$_exitcode`的值為`0`。 改變程序，返回值改為`1`： int main(void) { return 0; } 接著調試： [root@localhost nan]# gdb -q a Reading symbols from a...done. (gdb) start Temporary breakpoint 1 at 0x400478: file a.c, line 3. Starting program: /home/nan/a Temporary breakpoint 1, main () at a.c:3 3 return 1; (gdb) (gdb) n 4 } (gdb) 0x00000034e421ed1d in __libc_start_main () from /lib64/libc.so.6 (gdb) Single stepping until exit from function __libc_start_main, which has no line number information. [Inferior 1 (process 2603) exited with code 01] (gdb) p $_exitcode $1 = 1 可以看到打印的`$_exitcode`的值變為`1`。 參見[gdb手冊](https://sourceware.org/gdb/onlinedocs/gdb/Convenience-Vars.html). ## 貢獻者 nanxiao