Untyped arguments in a C function declaration

Recently I've been looking at the some of the C example code from the online resources of Steven Skiena's "Algorithm Design Manual" and have been baffl开发者_如何学JAVAed by the syntax of some of his function calls. Admittedly it's been a while since did C at uni but I've never encountered untyped function arguments like this:

find_path(start,end,parents)
int start;
int end;
int parents[];
{
    if ((start == end) || (end == -1))
        printf("\n%d",start);
    else {
        find_path(starts,parents[end],parents);
        printf(" %d",end);
    }
}

Is this valid syntax anymore? Are / were there any benefits with this style of function declaration? It seems more verbose than the conventional inline typing of arguments.

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They are called K&R style definitions. Don't use them in new code. Even K and R recommend that you stay away from them in "The C Programming Language 2ed".

A note of history: the biggest change between ANSI C and earlier versions is how functions are declared and defined.

The parameters are named between the parentheses, and their types are declared before opening the left brace; undeclared parameters are taken as int.

The new syntax of function prototypes makes it much easier for a compiler to detect errors in the number of arguments or their types. The old style of declaration and definition still works in ANSI C, at least for a transition period, but we strongly recommend that you use the new form when you have a compiler that supports it.

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This is an old style way of giving the function types. It was dropped in the C99 standard and is not appropriate for modern code.

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The arguments are typed, just not inline. The types are between the first line and the opening bracket.

Anyway, this style is old and not recommended.

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These K&R definitions are the historically traditional way to define functions. In the original C this was the only way to define a function.

Don't use K&R definitions any more. Why not? Because doing so stops the compiler being able to check for type mismatches.

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This old syntax stems from the typeless B programming language (and as others stated, is not in standard C anymore):

printn(n,b) {
    extrn putchar;
    auto a;

    if(a=n/b) /* assignment, not test for equality */
        printn(a, b); /* recursive */
    putchar(n%b + '0');
}

By the way, some compilers may offer a flag that let you compile this oldstyle K+R code.