GCC C++ STL 漂亮的打印机 - 手动调用并仅要求大小

Question

如何在 gdb 中手动调用 StdDequePrinter 以获取 gdb.parse_and_eval(('ed 变量？
为什么StdDequePrinter等没有只查询容器大小的功能？

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