这个奇怪的函数定义意味着什么？

Question

I came across this C program in a blog post :

main()
{
    int n;
    n = 151;
    f(n);
}

f(x)
int x;
{
    printf("%d.\n", x);
}

The post doesn't explain it. Can anybody explain what this weird function definition means?

Answer 1

This is the K&R style of C code, it's still valid C syntax, but I suggest you not using it in new-written code.

f(x)
int x;

is equivalent to ANSI C:

void f(int x)

---

K&R C is the C language described in the first edition of the book C programming language by Brian Kernighan and Dennis Ritchie, and named after the two authors. The second edition of the book updated to use ANSI C.

Answer 2

f(x)
int x;
{
    printf("%d.\n", x);
}

is an older way of defining function. Now it can be read as

void f(int x)
{
    printf("%d.\n", x);
}

Answer 3

This code is simply bad.

1. Obsolete declaration of function f()
2. There should be forward declaration of f() before main()
3. Return type is missing for f()

Answer 4

please change your c learning source!

that is a very old style of C (K&R C).

f(x)

int x;
{}

is equivalent to

void f(int x)
{}

you should really not wasting time learning that.

look for sources that teach ANSI C C89/C90 and also note the new features of C99 (that isn't widely adopted by many compilers, so know the differences)

Answer 5

This is a very old style of coding. This doesn't work out in ANSI. Better use something like

void f(int x)
{
 ... ... ...;/*Whatever is required*/
}