Argument type with default promotion?? What's that?

[svar]

Anyone understands what's wrong here? Just a simple thing, define a struct and a function set returning a variable
of that struct test type.

typedef struct{float var1;
}test;

test set();

main(){
test v1;
v1=set(1.0);
}
test set(float myval){
test t1 ;
t1.var1=myval;
return t1;}

This fails to compile with:

10: conflicting types for `set'
10: an argument type that has a default promotion can't match an empty parameter name list declaration
4: previous declaration of `set

 

[Salem]

I'd say you're compiling your C code with a C++ compiler.

> test set();
In C++, this means
test set( void );

In C, an empty function declaration basically means any parameters (which are also unchecked as well).


Since you're really passing a float, that doesn't match.

Be more precise with your function prototype, so it matches your function definition.

--

 

[svar]

No, I am using gcc(or do I need to disable C++?)

gcc -Wall vtest.c -o vtest.e
vtest.c:6: warning: return type defaults to `int'
vtest.c: In function `main':
vtest.c:9: warning: control reaches end of non-void function
vtest.c: At top level:
vtest.c:10: conflicting types for `set'
vtest.c:10: an argument type that has a default promotion can't match an empty parameter name list declaration
vtest.c:4: previous declaration of `set'

 

[svar]

BTW, with the change you suggest, the code works
so the question is: Does gcc need C++ explicitly turned off
if you want plain C code(Of course you can prototype to keep both C and C++ happy)?

 

[Salem]

> so the question is: Does gcc need C++ explicitly turned off
No, you're doing the other correct thing, which is using -Wall in your command line

As you note, you're using a C compiler in a particularly strict mode with the -Wall flag

For maximum diagnostics, use
[tt]gcc -W -Wall -ansi -pedantic -O2 prog.c[/tt]

--

 

[ArkM]

Some explanation added:
Default promotion in that case (in C and C++) means: convert float to double when passing an arg to a function without prototype (or with ... in parameters list).
It's one of default data type conversions (another examples is short to int or char to int). Promotion term - from shorter types to longer types...