如何在gdb中「觀察」C++ std :: vector的大小？

Question

我有一個std :: vector作爲類的一部分，它包含一個自定義類型。它的內容似乎在程序中某處發生了神祕的變化。我無法弄清楚發生了什麼。

有沒有辦法從gdb中「觀察」std :: vector的內容（或大小）？

謝謝。

Answer 1

有沒有辦法從gdb中「觀察」std :: vector的內容（或大小）？

假設您正在使用GCC，請在theVector->_M_impl._M_start和_M_finish上設置觀察點。如果您正在使用其他std :: vector實現，請相應地進行調整。

例子：

#include <vector> 

int main() 
{ 
    std::vector<int> v; 

    v.push_back(1); 
    v.push_back(2); 
} 

g++ -g t.cc 
gdb -q ./a.out 

Reading symbols from /tmp/a.out...done. 
(gdb) start 
Temporary breakpoint 1 at 0x40090f: file t.cc, line 5. 

Temporary breakpoint 1, main() at t.cc:5 
5  std::vector<int> v; 
(gdb) n 
7  v.push_back(1); 
(gdb) p v._M_impl._M_start 
$1 = (int *) 0x0 
(gdb) p v._M_impl._M_finish 
$2 = (int *) 0x0 
(gdb) p &v._M_impl._M_finish 
$3 = (int **) 0x7fffffffd878 
(gdb) watch *$3 
Hardware watchpoint 2: *$3 
(gdb) p &v._M_impl._M_start 
$4 = (int **) 0x7fffffffd870 
(gdb) watch *$4 
Hardware watchpoint 3: *$4 
(gdb) c 
Hardware watchpoint 3: *$4 

Old value = (int *) 0x0 
New value = (int *) 0x604010 
std::vector<int, std::allocator<int> >::_M_insert_aux (this=0x7fffffffd870, __position=0x0) at /usr/include/c++/4.4/bits/vector.tcc:365 
365  this->_M_impl._M_finish = __new_finish; 
(gdb) bt 
#0 std::vector<int, std::allocator<int> >::_M_insert_aux (this=0x7fffffffd870, __position=0x0) at /usr/include/c++/4.4/bits/vector.tcc:365 
#1 0x0000000000400a98 in std::vector<int, std::allocator<int> >::push_back (this=0x7fffffffd870, __x=@0x7fffffffd88c) at /usr/include/c++/4.4/bits/stl_vector.h:741 
#2 0x0000000000400935 in main() at t.cc:7 
(gdb) c 
Hardware watchpoint 2: *$3 

Old value = (int *) 0x0 
New value = (int *) 0x604014 
std::vector<int, std::allocator<int> >::_M_insert_aux (this=0x7fffffffd870, __position=0x0) at /usr/include/c++/4.4/bits/vector.tcc:366 
366  this->_M_impl._M_end_of_storage = __new_start + __len; 
(gdb) bt 
#0 std::vector<int, std::allocator<int> >::_M_insert_aux (this=0x7fffffffd870, __position=0x0) at /usr/include/c++/4.4/bits/vector.tcc:366 
#1 0x0000000000400a98 in std::vector<int, std::allocator<int> >::push_back (this=0x7fffffffd870, __x=@0x7fffffffd88c) at /usr/include/c++/4.4/bits/stl_vector.h:741 
#2 0x0000000000400935 in main() at t.cc:7 

... etc... 

Answer 2

我認爲http://sourceware.org/gdb/wiki/STLSupport會有所幫助。