How To Demangle C++ Symbols

One of the challenges that come with working with C++ code is dealing with “mangled” symbols.

These symbols are used by the C++ compiler to encode names of functions, variables, and other symbols.

Demangling symbols is the process of converting these encoded symbols into a human-readable format to make them easier to understand. In this tutorial, we’ll go over how to demangle C++ symbols.

Steps:

Step 1: Identify the mangled symbol

The first step in demangling a C++ symbol is to identify the mangled symbol. This can usually be found in compiler error messages, stack traces, and other debugging outputs. The symbol will look something like this: _Z7averageii.

Step 2: Use a demangling tool

There are several demangling tools available that can convert mangled symbols into human-readable format. One such tool is c++filt, which is a command-line utility that comes with most C++ compilers. To use c++filt, simply pass the mangled symbol as an argument and the tool will output the demangled version. For example:

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$ c++filt _Z7averageii
average(int, int)

Another option is to use an online demangler tool such as Demangler.com, which provides a simple interface for decoding mangled symbols online.

Step 3: Demangle in code

If you need to demangle C++ symbols in your code, you can use a demangling library such as abi::__cxa_demangle. This library is part of the C++ ABI (application binary interface) and is available on most modern C++ compilers.

To demangle a symbol using abi::__cxa_demangle, you’ll need to pass a mangled symbol as the first argument, a buffer to store the demangled symbol as the second argument, the size of the buffer as the third argument, and a pointer to an integer to store the demangled length as the fourth argument. Here’s an example:

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#include <cstdlib>
#include <iostream>
#include <cxxabi.h>
 
int main() {
    const char* mangled = "_Z7averageii";
    int status;
    char* demangled = abi::__cxa_demangle(mangled, NULL, NULL, &status);
 
    if (status == 0) {
        std::cout << demangled << std::endl;
        std::free(demangled);
    } else {
        std::cerr << "Error: could not demangle symbol" << std::endl;
    }
 
    return 0;
}

This code snippet shows how to use abi::__cxa_demangle to demangle a symbol. The status variable is used to check if the demangling was successful, and the free function is used to release the memory allocated for the demangled symbol.

Output:

average(int, int)

Conclusion:

Demangling C++ symbols is a useful skill to have when working with C++ code. By following the steps outlined in this tutorial, you can easily decode mangled symbols into a human-readable format using tools like c++filt or demangling libraries like abi::__cxa_demangle.