std :: string上的分段錯誤

Question

我正在運行一個應用程序，由於分段錯誤而停止在一個點上。 我將嘗試登記環境： - 應用程序有一個包含std :: string成員（數據）的類（Generator），並且該成員已正確初始化爲「HelloWorld」。 - 此對象的指針傳遞給另一個類（Product）的成員函數（send1）。只要我嘗試在函數內部打印數據的值，就會導致分段錯誤。如果我在調用send1函數之前嘗試打印數據的值，它會正確打印。

下面是GDB輸出：

(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) 

這裏是Valgrind的輸出

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. 

這實際上是一個更大的應用程序的一部分，但我已經剝離了應用，並使其非常小，所以我可以很容易地調試這個問題，但即使現在我也不知道爲什麼會出現這個問題。使用gdb我試圖檢查內存佈局，但在調用函數之前和之後內存地址和內容看起來完好無損。事實上，如果我試圖使用gdb打印功能打印數據的值，它會出現是正確的。我已經嘗試了很多事情，比如在堆上分配內存等，但似乎沒有任何工作。請求您親切指導我如何開始調試此問題。

Answer 1

我最好的猜測是genptr已被刪除/銷燬，但它所使用的內存在調試器中打印出genptr-> data的內容時尚未被覆蓋。然而，ostream operator<<函數在內部分配了一些內存，並且恰好重複使用了相同的空間，所以它被實際上的時間覆蓋並嘗試打印字符串，導致崩潰。

您可以通過查看SEGV後0x9917020（其中genptr指向的內存）的內存來查看它是否已更改。你應該能夠在上面的最後gdb提示符下執行up，然後執行p genptr->data。

Answer 2

很高興看到send1的聲明和實現，否則很難提供幫助。產品/發電機有任何虛擬功能嗎？

爲什麼寫COUT < < 「數據=」 < <這 - >數據< < ENDL;而不僅僅是數據？這有什麼區別嗎？

嘗試更改Product :: send1（Generator * genptr）到Product :: send1（const Generator & gen），並用ptr-> send1（* this）調用它，看看是否有同樣的問題。