Printing C++ class objects with GDB

Question

Is there some \"default function\" to print an object like a string on the GDB when we are debugging C++ applications? Something like: toString();

Or my class have t

Answer 1

Define operator<< and call it from GDB

C++ equivalent of Java's toString? was mentioned in the comments, and operator<< is the most common way of defining a to string method on a class.

This is likely the sanest approach because the resulting string method will be part of the codebase itself, and so:

• it is less to stop compiling (one would hope!)
• it is readily available without any GDB setup
• it can be called from C++ itself when needed

Unfortunately I haven't found a completely sane way of calling operator<< from GDB, what a mess: calling operator<< in gdb

This has worked on my hello world test:

(gdb) call (void)operator<<(std::cerr, my_class)
MyClass: i = 0(gdb)

There is no newline at the end, but I can live with that.

main.cpp

#include 

struct MyClass {
    int i;
    MyClass() { i = 0; }
};

std::ostream& operator<<(std::ostream &oss, const MyClass &my_class) {
    return oss << "MyClass: i = " << my_class.i;
}

int main() {
    MyClass my_class;
    std::cout << my_class << std::endl;
}

Compiled with:

g++ -ggdb3 -O0 -std=c++11 -Wall -Wextra -pedantic -o main.out main.cpp

Tested in GDB 8.1.0, Ubuntu 18.04.