Constructors have no return value. Still, a constructor sometimes must propagate the failure. There are several method for this: error flags, like in ios_base, globals, like errno in C, and most importantly exceptions. However exceptions in constructors have special behaviour.

// error detection with member:

void f()
{
    ifstream inp( "input.dat" );

    if ( ! inp ) ...
    ...
}


//==============================================

// use exceptions for constructors
class X;

int main()
{
    try
    {
        X *xp = new X();
    }
    catch( ...) { /* space allocated, but xp was not set */ }
    // still no problem: system deallocate space
}


// but:
class X
{
public:
    X(int i) { p = char[i]; init(); }
    ~X() { delete [] p; }       // must not throw exception
private:
    void init() { ... throw ... }   // BAD: destructor won't run !
    char *p;                        // constructor was not completed
};


//===============================================

// member initialization

class Y
{
public:
    Y(int i, int j) : x(i), z(j) { }  // x(i) or z(j) throws exception
                                      // but Y must not emit any
private:
    X x;
    Z z;
};

class Y
{
public:
    Y(int i, int j)
    try
        : x(i), z(j)    // x(i) or z(j) throws exception
    { }
    catch( ... )
    {
        // we get here if either x(i) or z(j) throws exception
        // if x(i) throws, then z uninitialized
        // if z(j) throws, then ~X::X() has already executed

        // what to do here ?? 
    }
private:
    X x;
};



#include <iostream>

class X
{
public:
    X() { throw 1; }
};
class Y
{
public:
    Y()
    try
        : x()
    { }
    catch( ... ) { /* throw; */ }
private:
    X x;
};

int main()
try {
    Y y;
    return 0;
}
catch (int i)
{
std::cerr << "exception: " << i << std::endl;
}

// if a subobject initializer throws exception : thet subobject has
// not been created: no object without subobject, so constructor
// will throw exception !