How is this pre-standard function declaration compiled with modern compiler?

Question

I found the following declaration code in the very early sources of C compiler

main(argc, argv)
int argv[]; { 
   return 0;
}

I tried to run it on ideone.com compiling it in "C" mode with gcc-4.7.2 and it compiles fine and even runs successfully

result: Success     time: 0s    memory: 1828 kB     returned value: 0

Now I'm aware that there was a pre-standard way of declaring function parameters this way:

int funct(crc, buf, len)
    int crc;
    register char* buf;
    int len;
{
   //function implementation
}

but in the latter style it's quite clear - the parameters are first just listed, then declared as if they were a kind of local variables and I see all the parameters declared and the return type.

Back to the first code

main(argc, argv)
int argv[]; { 
   return 0;
}

in the former code there're two parameters listed and only one declared and it looks like argv has type array of int.

How is it being treated by the compiler?

Answer 1

You are talking about pre-ANSI C, and the style of prototype known as K&R prototypes. For such function declarations, parameters and return values whose types are not specified are deemed to be of type int.

Answer 2

It is K&R C syntax where compiler won't check the types of arguments and arguments will be default to int.

K&R sysntax still gets suppot from the latest compilers for compatibility.In cases where code must be compilable by either standard-conforming or K&R C-based compilers, the STDC macro can be used to split the code into Standard and K&R sections to prevent the use on a K&R C-based compiler of features available only in Standard C.