Try-catch doesn't work in shared library?

Question

_{(This is like my other question but this one is for another thing, even if it\'s related)}

I\'ve got a big issue in my project. I\'ve got a library which handl

Answer 1

According to gcc manual:

if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ or GCJ driver, as appropriate for the languages used in the program, or using the option -shared-libgcc, such that it is linked with the shared libgcc.

Shared libraries (in C++ and Java) have that flag set by default, but not main executables. In any case, you should use it on both.

Test Case:

lib.cpp:

#include "lib.hpp"
#include <string>
#include <iostream>

using namespace std;

int function_throws_int() {
    try {
        throw 2;
    }
    catch (...) {
        cout << "int throws lib" << endl;
        throw;
    }

    return -1;
}

int function_throws_string() {
    try {
        throw std::string("throw");
    }
    catch (...) {
        cout << "throws string lib" << endl;
        throw;
    }
}

lib.hpp:

int function_throws_int();
int function_throws_string();

Compile command line: g++ -m64 -g -shared-libgcc -shared -fPIC -std=c++11 -o libtest.so lib.cpp

main.cpp:

#include "lib.hpp"
#include <string>
#include <iostream>

using namespace std;

int main(int argc, char ** argv) {
    try {
        function_throws_int();
    }
    catch (const string & e) {
        cout << "string caught main" << endl;
    }
    catch (int i) {
        cout << "int caught main" << endl;
    }

    return 0;
}

Compile command line: g++ -m64 -g -shared-libgcc -o main -L. main.cpp -ltest

Execute: LD_LIBRARY_PATH=. ./main

Output:

int throws lib
int caught main

Answer 2

Simple. Never use ld with C++. I changed all ld commands in my project to g++ but seems I forgot for this library.

In short, I was using ld for building my library but g++ for the main executable. So the exceptions worked in the executable but not in the library because ld does not includes the C++ libraries which handle the exception system.