Programming

Hi,

I have one doubt, in the below program, if I declare char *b inside the main(), the function compiles & runs properly. But at the same time, if I declare it globally it compiles but when we run it, it creates core dump (segmentation fault) both in C & C++. It is not being trapped by catch handler also. Do you know why?

char *b;

int main(){
//char *b;
try {
cout << "Enter char: ";
//cin >> b;
scanf("%c", b);
cout << b << endl;
} catch(...) {
cout<<"An Exception has occured"<<endl;
}
}

C does not have try ... catch.

One thing is for sure since you do not allocate memory for 'char *b', it is (surely) pointing to an invalid area thus the coredump ... To remove any doubt just try changing 'char *b' to 'char b[1]' and spot the difference

The answers you gave doesn't answered my question. Ok, let's take it as it was compiled using C++ compiler, though it was not trapped using the catch() handler. And also my question hovers around declaring "b" in global and local scope. So please explain where the original problem lies.

Code:

char *b;   /* =NULL */
....
cin >> *b;

means read a string to a null pointer?

yes, that answered my question. Since the global variable stored in the data segment of BSS (Block Started by Symbol) memory area, it gets initialized to NULL (0 in precise), if not explicitly initialized while declaration. So writing to that memory causes Segmentation Fault core dump. And the local variable gets stored in the stack, which is initialized to some garbage value. so writing to that memory does not cause any core dump.

Thanks porter.

Hi, if I instantiate a local static object of type class A, inside a function foo() will the constructor of class A be called whenever I invoke this function or will it be invoked during program start-up automatically and only once? Also does the program behavior change in calling constructor if the function foo() is declared global function or not?