C++ Exception with Callstack

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Table of Contents

• C++23 Exception Class with Callstack
• C++ Exception Class with Callstack (Windows only)
• History

The example code is hosted on Github.

I developed two C++ exception classes that could tremendously help troubleshoot customer problems not reproducible on the developer's system and a common function is called and you do not know its caller because they are numerous. The customer must be given an executable and a pdb built with that executable to get the correct call stack. A pdb file contains the debug symbols. You cannot give a pdb built later from the same code. When we build the executable, every function is given an address offset. The pdb is based on those offsets. When the binary is built again, the offsets change. In short, the pdb's function offsets have to match the executable.

C++23 Exception Class with Callstack

C++23 Standard ratified this year has introduced a stacktrace class that retrieves the call stack trace. The stacktrace can aid in troubleshooting during exceptions. Therefore, I derived Cpp23ExceptionWithCallstack from std::runtime_error and added stacktrace as a member to get the trace information. My stacktrace usage heavily relies on Stephan T. Lavavej’s Godbolt example.

Here is an example of how to use Cpp23ExceptionWithCallstack.

#include <iostream>
#include "Cpp23ExceptionWithCallstack.h"

using namespace std;

int inner(const int n) 
{
    if (n < 0) 
    {
        throw Cpp23ExceptionWithCallstack{"Error"};
    }
    return n * n;
}

int outer(const int n) 
{
    return inner(n);
}

int main() 
{
    try 
    {
        cout << outer(-5) << "\n";
    }
    catch (const Cpp23ExceptionWithCallstack& except) 
    {
        cout << except.GetCallstack() << std::endl;
    }
    return 0;
}

The call stack output is as follows. Make sure to put the executable’s pdb file in the same folder to get function names, filenames and line numbers in the output.

Cpp23CallStack!inner+0x3A, D:\GitHub\cpp_show_callstack\Cpp23CallStack\Cpp23CallStack.cpp(11)
Cpp23CallStack!outer+0x29, D:\GitHub\cpp_show_callstack\Cpp23CallStack\Cpp23CallStack.cpp(18)
Cpp23CallStack!main+0x37, D:\GitHub\cpp_show_callstack\Cpp23CallStack\Cpp23CallStack.cpp(22)
Cpp23CallStack!invoke_main+0x39, D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl(79)
Cpp23CallStack!__scrt_common_main_seh+0x12E, D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl(288)
Cpp23CallStack!__scrt_common_main+0xE, D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl(331)
Cpp23CallStack!mainCRTStartup+0xE, D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_main.cpp(17)
KERNEL32!BaseThreadInitThunk+0x1D, unknown(0)
ntdll!RtlUserThreadStart+0x28, unknown(0)

C++ Exception Class with Callstack (Windows only)

What if you are not using C++23? Fret not. I have another C++ exception class, CppExceptionWithCallstack, based on StackWalker, created by Jochen Kalmbach, that relies on the Windows debugging API to do its work. In the beginning, I encountered a weird problem when my StackWalker derived class printed the full call stack in the first run and only the first function printed in the subsequent runs. I debugged the problem and found nothing is wrong in its operations: it reports no function caller after the first one. I filed this issue at StackWalker GitHub. Since then, I use StackWalker directly instead of deriving from it, I do not have this problem. If you encounter the same problem, please let me know.

Here is an example of how to use CppExceptionWithCallstack.

#include <iostream>
#include "CppExceptionWithCallstack.h"

using namespace std;

int inner(const int n) 
{
    if (n < 0) 
    {
        throw CppExceptionWithCallstack{"Error"};
    }
    return n * n;
}

int outer(const int n) 
{
    return inner(n);
}

int main() 
{
    try 
    {
        cout << outer(-5) << "\n";
    }
    catch (const CppExceptionWithCallstack& except) 
    {
        cout << except.GetCallstack() << std::endl;
    }
    return 0;
}

This is the call stack output. Do note that, as mentioned above, you must put the executable’s pdb file in the program’s folder to get the function names, filenames and line numbers in the output.

D:\GitHub\cpp_show_callstack\WinCallStack\StackWalker.cpp (1140): StackWalker::ShowCallstack
D:\GitHub\cpp_show_callstack\WinCallStack\CppExceptionWithCallstack.h (19): CppExceptionWithCallstack::CppExceptionWithCallstack
D:\GitHub\cpp_show_callstack\WinCallStack\WinCallStack.cpp (10): inner
D:\GitHub\cpp_show_callstack\WinCallStack\WinCallStack.cpp (18): outer
D:\GitHub\cpp_show_callstack\WinCallStack\WinCallStack.cpp (24): main
D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl (79): invoke_main
D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl (288): __scrt_common_main_seh
D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl (331): __scrt_common_main
D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_main.cpp (17): mainCRTStartup
00007FFF7E7226AD (KERNEL32): (filename not available): BaseThreadInitThunk
00007FFF7F14AA68 (ntdll): (filename not available): RtlUserThreadStart

History

• 14^th August 2023: First release