C＆C ++中main的区别是什么

Question

What is the difference between main in a C program and in a C++ program?

Other than

1. return statement ( default 1 in C,`0 in C++)

2. syntax:

    int main() { /* … */ } int main(int argc, char* argv[]) { /* … */ } int main() , void main() ,etc ... 

Mainly:

1. difference between main in C Program & C++ program

2. Are there any differences between C++98, C++03 and C++0x according to the ISO standard? ie program's entry point (program startup implementation), etc.

Answer 1

In modern C, and modern C++:

• main is always either int main() or int main(int, char*[]) .
• In C89, you have to return from main explicitly.
• In C99 and C++, if you don't return explicitly, you implicitly return 0 .

[ (I've checked the C99 standard now and edited this paragraph.) ] For your second question, in C99 you must have precisely one of the two main functions. In C++ the standard says that a program is well-formed if it has a main function that returns int , and that every conforming implementation must accept the two listed versions as an entry point (for a "hosted program", eg not for the Linux kernel); see 3.6.1. [/edit] To the best of my knowledge, calling conventions are also not part of the standard.

I don't understand your question about memory, but do note that neither C99 nor C++03 have anything but a rudimentary memory model, whereas the new C++0x explicitly adds a memory model in order to enable well-defined concurrent and atomic operations.

Answer 2

In C, as opposed to C++, main can be called recursively.

/* valid C */
#include <stdio.h>
int main(int argc, char **argv) {
  putchar(argc ? '.' : '\n');
  if (argc == 0) return 0;
  return main(argc - 1, NULL);
}

Answer 3

C99 and C++ are put in line for the definition of main in hosted environments. There are two function interfaces that are allowed

int main(void);
int main(int, char*[]);

Both languages allow the implicit return from main without return statement in which case a return value of EXIT_SUCCESS is returned to the caller.

Answer 4

Edit: Is there any difference in program startup implementation is there any difference in c++98,C++03,C+++0x main ,etc.........

Not in main . However, there is a huge difference in what happens before main is called in C versus C++. In C++, objects with static storage are typically initialized prior to entering main .

Note:
An implementation is allowed to perform dynamic initializations of static data in the midst of main , but it must do so prior to the first reference to that static data. I've never run across an implementation that takes advantage of this flexibility.