Question

示例代码：

int main()
{
        float x = 456.876;

        printf ("\nx = %f\n", x);

        return 0;
}

在gdb中，我执行了这样的代码：

Breakpoint 1, main () at sample_float.c:5   
5               float x = 456.876;   
(gdb) n    
7               printf ("\nx = %f\n", x);   
(gdb) p &x   
$1 = (float *) 0x7fffffffd9dc   
(gdb) x/4fb &x   
0x7fffffffd9dc: 33      112     -28     67

是否可以使用：x / fb命令查看x的地址值：456.876？

感谢。

Answer 1

也许我误解了你的问题，但你可以做到

p/f x

或者

x/f &x

那是你在找什么？

Answer 2

同意上述答案，但要明白为什么你得到了你所做的结果。

(gdb) x/4fb &x   
0x7fffffffd9dc: 33      112     -28     67

来自gdb手册

x/3uh 0x54320' is a request to display three halfwords (h) of memory, formatted as unsigned decimal integers ( u'），从地址0x54320开始。

因此，x / 4fb＆amp; x将一个字节格式化为float 4次。不 4个字节作为浮点数。

Answer 3

Here is a link to examining memory using gdb

You can use the command x (for "examine") to examine memory in any of several formats, 
independently of your program's data types.

x/nfu addr
x addr
x
n, f, and u are all optional parameters that specify how much memory to display and how to format it; addr is an expression giving the address where you want to start displaying memory. If you use defaults for nfu, you need not type the slash `/'. Several commands set convenient defaults for addr.

n, the repeat count

The repeat count is a decimal integer; the default is 1. It specifies how much memory (counting by units u) to display.

f, the display format

The display format is one of the formats used by print, `s' (null-terminated string), or `i' (machine instruction). The default is `x' (hexadecimal) initially. 
The default changes each time you use either x or print.

 u, the unit size The unit size is any of
 b: Bytes.
 h: Halfwords (two bytes).
 w: Words (four bytes). This is the initial default.
 g: Giant words (eight bytes).

分析gdb中的浮点值

3 个答案: