C 5.71 functions Prototype / declaration error

Hi

I am using the new compiler version 5.71 and have the following problem.

if I create a function as follows :-

int Scan_Test(int,int,FILE);

int Scan_Test(int v1,int v2, FILE *tempfile)
{
do something
}

The compiler responds with the following error :-
prototype and old style parameters mixed.
function prototype formal ‘FILE’ needs type or class

if I use the prototype :-
int Scan_Test();
Then the compiler compiles OK but responds with :-
Deprecated declaration Scan_Test() – give arg types

How do I stop the compiler from complaining.
only functions that contain the FILE parameter cause this problem?.

TIA

Terry

The problem is that you’ve missed off the * in the prototype. So instead of declaring a function which takes a pointer to a FILE struct, you’ve declared a function which takes a FILE struct by value (i.e. a copy of it). For this to work the compiler needs to have seen the full definition of FILE, so that it can work out its size (so that it knows how much stack space is needed to store it when passing it into the function). But the full definition hasn’t been seen, hence the “…formal ‘FILE’ needs type or class” error.

Exactly why the error message starts off with a “prototype and old style parameters mixed” error I’m not sure, but the missing * is the cause of the problems.

The basic rule you should follow with function prototypes in C/C++ is to make them exactly the same as the declaration. The variable names can be omitted if you wish (the compiler doesn’t need to know them for the prototype), but keeping them there will be a useful reminder for any fleshy types who want to use your code (including yourself).

Note that there are some times when a function prototype shouldn’t be the same as the declaration, e.g. when declaring static class member functions, but more often than not the declaration must be the same as the prototype for things to work correctly, if at all.

Hi

I did try that before I posted an got the following errors? :-(

int Scan_Test(int,int,FILE*);

Causes the following:-

prototype and old style parameters mixed
expected ‘)’ or ‘,’ – inserted ‘)’ before ‘*’
function prototype formal ‘FILE’ needs type or class

expected ‘;’ or ‘,’ – inserted ‘;’ before ‘*’
expecting declarator or type but found ‘)’

I also tried

int Scan_Test(int,int,FILE *tempfile);

but that does not work either ?

TIA

Terry

In that case you probably forgot to #include <stdio.h>. Even though you’re only passing around a pointer to it, the compiler still wants to know what type it is.

Hi

Thanks for that, so easy when someone else points it out.

I had moved some includes around and moved stdio.h

I could get to compile with errors but have found that these errors
come back to haunt me later so I would rather sort them out now.

Thanks again for your help

Terry

For what it’s worth, I don’t see any value in doing the old-style prototypes which don’t name the parameters; it’s not beneficial to anyone (even you in the future) who needs to use them because they have to go off and look at the function implementation to understand it – it’s far better to give your function parameters sensible names and then use an identical function signature as your prototype.