std :: string上的分段错误

时间:2012-01-18 18:31:02

标签: c++ segmentation-fault

我正在运行一个由于分段错误而在某一点停止的应用程序。 我将尝试争取环境:   - 应用程序有一个类(Generator),它包含一个std :: string成员(数据),这个成员正式初始化为“HelloWorld”。   - 此对象的指针传递给另一个类(Product)的成员函数(send1)。一旦我尝试在函数内打印数据值,它就会给出分段错误。如果我在调用send1函数之前尝试打印数据值,则会正确打印。

这是gdb输出:

(gdb) br Generator::test
Breakpoint 1 at 0x80499ef: file ../app/generator/src/generator.cpp, line 58.
(gdb) br Product::send1
Breakpoint 2 at 0x804a17e: file ../app/configurator/src/product.cpp, line 43.
(gdb) run
[Thread debugging using libthread_db enabled]
[New Thread -1208071520 (LWP 18389)]
[Switching to Thread -1208071520 (LWP 18389)]

Breakpoint 1, Generator::test (this=0x9917020) at ../app/generator/src/generator.cpp:58
58                 cout << "data = " << this->data << endl;
(gdb) n
data = HelloWorld
59                 Product* ptr = new Product;
(gdb) n
60                 bool status = ptr->send1( this );
(gdb) s

Breakpoint 2, Product::send1 (this=0x99170c8, genptr=0x9917020) at ../app/configurator/src/product.cpp:43
43              cout << genptr->data << endl;
(gdb) p genptr->data 
$1 = {static npos = 4294967295, 
  _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
    _M_p = 0x99170b4 "HelloWorld"}}
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
0x076751e6 in std::operator<< <char, std::char_traits<char>, std::allocator<char> > () from /usr/lib/libstdc++.so.6
(gdb) bt
#0  0x076751e6 in std::operator<< <char, std::char_traits<char>, std::allocator<char> > () from /usr/lib/libstdc++.so.6
#1  0x0804a19a in Product::send1 (this=0x99170c8, genptr=0x9917020) at ../app/configurator/src/product.cpp:43
#2  0x08049a85 in Generator::test (this=0x9917020) at ../app/generator/src/generator.cpp:60
#3  0x08048f4c in Configure::init (this=0x9917008) at ../app/configurator/src/configurator.cpp:89
#4  0x08048c93 in main (argc=1, argv=0xbfed7364) at ../launch/main/src/appLaunch.cpp:20
(gdb) 

这是valgrind输出

valgrind --tool=memcheck --leak-check=yes ./application 
==18328== Memcheck, a memory error detector.
==18328== Copyright (C) 2002-2005, and GNU GPL'd, by Julian Seward et al.
==18328== Using LibVEX rev 1575, a library for dynamic binary translation.
==18328== Copyright (C) 2004-2005, and GNU GPL'd, by OpenWorks LLP.
==18328== Using valgrind-3.1.1, a dynamic binary instrumentation framework.
==18328== Copyright (C) 2000-2005, and GNU GPL'd, by Julian Seward et al.
==18328== For more details, rerun with: -v
==18328== 
data = HelloWorld
==18328== Invalid read of size 4
==18328==    at 0x76751E6: std::basic_ostream<char, std::char_traits<char> >& std::operator<< <char, std::char_traits<char>, std::allocator<char> >(std::basic_ostream<char, std::char_traits<char> >&, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) (in /usr/lib/libstdc++.so.6.0.3)
==18328==    by 0x804A199: Product::send1(Generator*) (product.cpp:43)
==18328==    by 0x8049A84: Generator::test() (generator.cpp:60)
==18328==    by 0x8048F4B: Configure::init() (configurator.cpp:89)
==18328==    by 0x8048C92: main (appLaunch.cpp:20)
==18328==  Address 0x5C040234 is not stack'd, malloc'd or (recently) free'd
==18328== 
==18328== Process terminating with default action of signal 11 (SIGSEGV)
==18328==  Access not within mapped region at address 0x5C040234
==18328==    at 0x76751E6: std::basic_ostream<char, std::char_traits<char> >& std::operator<< <char, std::char_traits<char>, std::allocator<char> >(std::basic_ostream<char, std::char_traits<char> >&, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) (in /usr/lib/libstdc++.so.6.0.3)
==18328==    by 0x804A199: Product::send1(Generator*) (product.cpp:43)
==18328==    by 0x8049A84: Generator::test() (generator.cpp:60)
==18328==    by 0x8048F4B: Configure::init() (configurator.cpp:89)
==18328==    by 0x8048C92: main (appLaunch.cpp:20)
==18328== 
==18328== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 17 from 1)
==18328== malloc/free: in use at exit: 159 bytes in 5 blocks.
==18328== malloc/free: 5 allocs, 0 frees, 159 bytes allocated.
==18328== For counts of detected errors, rerun with: -v
==18328== searching for pointers to 5 not-freed blocks.
==18328== checked 116,636 bytes.

这实际上是一个更大的应用程序的一部分,但我已经剥离了应用程序,并使其非常小,以便我可以轻松调试问题,但即使现在我不知道为什么这个问题发生。使用gdb我试图检查内存布局,但在调用函数之前和之后,内存地址和内容看起来完好无损。事实上,如果我尝试使用gdb打印功能打印数据的值,那么它就是正确的。我已经尝试了很多东西,比如在堆上分配内存等,但似乎没有任何工作。请您指导我如何开始调试此问题。

2 个答案:

答案 0 :(得分:1)

很高兴看到send1的声明和实现,否则很难提供帮助。产品/发电机是否有任何虚拟功能?

为什么要写cout&lt;&lt; “Data =”&lt;&lt; this-&gt; data&lt;&lt; ENDL;而不仅仅是数据?这有什么不同吗?

尝试将Product :: send1(Generator * genptr)更改为Product :: send1(const Generator&amp; gen)并使用ptr-> send1(* this)调用它,看看是否存在同样的问题。

答案 1 :(得分:0)

我最好的猜测是genptr已被删除/销毁,但是当你打印出调试器中genptr-&gt;数据的内容时,它所使用的内存还没有被覆盖。但是,ostream operator<<函数在内部分配了一些内存,并且恰好重用了相同的空间,因此它实际上会被覆盖并尝试打印字符串,从而导致崩溃。

您可以通过查看SEGV后面的0x9917020(其中genptr点)的内存并查看它是否已更改来检查此情况。您应该可以在上面的最终gdb提示符下执行up然后p genptr->data