[gcc c ++ stl漂亮打印机-手动调用并仅询问尺寸

Question

我如何在gdb中调用gdb.parse_and_eval（）编辑的变量的StdDequePrinter 手动？为什么StdDequePrinter等不具有仅查询容器的[[size的功能？

Answer 1

测试C ++程序

#include <stack>

int
main(
        int,
        char**)
{   std::stack<int> data;

    data.push(1);
    data.push(2);
    data.push(3);
    data.push(4);
    data.pop();
    return 0;
}

测试漂亮打印机：
import re

class Printer:
    "Print a std::deque"

    def __init__(self, val):
        self.typename = val.type.template_argument(0)
        self.val = val
        self.elttype = val.type.template_argument(0)
        size = self.elttype.sizeof
        if size < 512:
            self.buffer_size = int (512 / size)
        else:
            self.buffer_size = 1

        start = self.val['_M_impl']['_M_start']
        end = self.val['_M_impl']['_M_finish']

        delta_n = end['_M_node'] - start['_M_node'] - 1
        delta_s = start['_M_last'] - start['_M_cur']
        delta_e = end['_M_cur'] - end['_M_first']

        self.size = self.buffer_size * delta_n + delta_s + delta_e

    def calcSize(self):
        return int(self.size)

# use modified version of STL pretty printer to get the size()
value = gdb.parse_and_eval('data.c');
printer = Printer(value)
print (str(printer.calcSize()))

# how to get the original printer - but it can't print size value only
printer = gdb.default_visualizer(value)
print (str(printer))
printer.__init__(value.__class__.__name__,value)
print (str(printer.to_string()))

# get the size only
sizeOnly = re.search('.* with ([0-9]+) elements', printer.to_string(), re.IGNORECASE)
if sizeOnly:
    print(sizeOnly.group(1))

# no need to know stack is implemented on top of deque
value = gdb.parse_and_eval('data')
printer = gdb.default_visualizer(value)
print (str(printer))
printer.__init__(value.__class__.__name__,value)
print (printer.to_string())
sizeOnly = re.search('.* with ([0-9]+) elements', printer.to_string(), re.IGNORECASE)
if sizeOnly:
    print(sizeOnly.group(1))

输出：
Breakpoint 1, main () at ../main.cpp:19
19      data.push(4);
(gdb) source Debug/test.py
3
<libstdcxx.v6.printers.StdDequePrinter object at 0x7f543e0aee80>
Value with 3 elements
3
<libstdcxx.v6.printers.StdStackOrQueuePrinter object at 0x7f1f00bc7208>
Value wrapping: std::deque with 3 elements
3