一个为Linux编写的C函数没有返回值，C编译器如何处理呢？

Question

I get one program (written for linux originally). I can't understand the syntax of some functions. The functions have no return value type. Let me give one example

add_one_point(xx,yy,zz,index)
  float xx,yy,zz;
  int index;
{
 //the implementation 
}

In some functions, the implementations don't return any value, but some really return values. Is this a valid C code? If so, how does c compiler process that?

Thanks in advance! Jogging

Answer 1

Older versions of C allowed the return type to be omitted, defaulting it to int .

C99 no longer allows it, so if you compiled under C99 mode, it would fail.

Answer 2

You should declare a function not returning any value as returning void , and in any case the return type should be specified. Your compiler might allow you to compiler a function without return value specified (it will default to int, that is why that code might be/have been working), but a modern compiler will at least issue a warning.

Furthermore, as somebody else already noticed, also the input types are specified in an unusual way (without verifying, I would call it non-standard compliant)