Question

Please, tell me from where execution starts in c++, hope your answer is “from main”.

Then what about this?

class abc
{ 
public:
    abc()
    { 
        cout<<"hello";
    }
};

const abc obj;

int main( )
{ 
    cout<<"Main";
}

output:

helloMain 

Please elaborate.

Answer 1

From your comments to the other answers strut, it sounds like a 10,000 foot view might assist in understanding.

The exact steps involved in launching an application differs between OSes, compilers, and programming languages but the “general” process is essentially the same.

1. The OS kernel is asked to start a new process that runs the target executable
2. The kernel creates a new process to host the exectuable
3. The kernel sets up basic process attributes: File descriptors, environment variables, security attributes, etc.
4. The kernel runs a user-mode “loader” to actually open the file contianing the executable and get it ready for execution
5. The loader reads the file containing the executable and breaks it out into various segments: global variable data, executable code, etc
6. The loader resolves any dynamic-link library symbols and properly lays out memory for the executable code (essentially, this step involves making sure that all pointers in the program point to the proper locations)
7. The loder then invokes the “entry” function of the executable. However, this is not your ‘main’ function. The ‘entry’ function is usually hidden by the OS/compiler to allow for pre-main initialization code to run.
8. In the case of C++ the entry function will most likely look something like the following:

---

int __entry( int argc, char *argv[] )
{
    // configure standard I/O streams, threading tables, & other utilities
    initialize_c_runtime(); 

    // run the constructors for all static objects
    initialize_static_cplusplus_objects(); 

    // Now, finally, after *all* that we execute the 'main' function
    return main(argc, argv);
}