c++ - gdb: 当前上下文中没有符号 "tulip"

Question

我正在尝试编译我的程序并使其可执行，但每次我尝试打印它时都会说:“当前上下文中没有符号“郁金香”。"

这是我的代码:

#include <stdlib.h>
#include <stdio.h>

int main() {
unsigned long *daffodil = (unsigned long *) malloc(sizeof(unsigned long));
if (daffodil == (unsigned long *) NULL)
exit(EXIT_FAILURE);
*daffodil = 170;
unsigned long *tulip = daffodil;
unsigned long *carnation = (unsigned long *) malloc(sizeof(unsigned long));
if (carnation == (unsigned long *) NULL)
exit(EXIT_FAILURE);
*carnation = 995;
unsigned long *lily = tulip;
unsigned long crocus = 953;
unsigned long *zinnia = &crocus;
(void) printf("Registering daffodil: %lu.\n", *daffodil);
(void) printf("Registering tulip: %lu.\n", *tulip);
(void) printf("Registering carnation: %lu.\n",*carnation);
(void) printf("Registering lily: %lu.\n", *lily);
(void) printf("Registering crocus: %lu.\n", crocus);
(void) printf("Registering zinnia: %lu.\n", *zinnia);
carnation = (unsigned long *) NULL;
free(daffodil);
free(carnation);

return EXIT_SUCCESS;
}

这是我在终端中所做的:

Answer 1

为了在 GDB 中查看局部变量，您必须中断该函数内的程序执行。您正试图在程序终止后打印该值，但这是不可能的。

尝试在第 10 行放置一个断点，我认为:

(gdb) br 10
(gdb) run
(gdb) print tulip

您也可以在 main 的开头中断，然后继续前进直到变量初始化:

(gdb) br main
(gdb) run
(gdb) next
(gdb) next
(gdb) ...
(gdb) print tulip

main 处的断点非常频繁，以至于 gdb 有一个自动执行断点的命令:start。

如果你对某个变量特别感兴趣，那么你可以显示它，这样它就会在每一步自动打印:

(gdb) start
(gdb) display tulip
(gdb) next
(gdb) next
(gdb) ...