Data type Qualifers

[Kuljit]

Hello everyone,

What are data type qualifers?

- Kuljit Singh Tomar
..

 

[Ben Pfaff]

What are data type qualifers?

const, restrict, and volatile

 

[Rod Pemberton]

const, restrict, and volatile

Type qualifiers modify the way the data is used or accessed. Many
non-standard "attributes" are implemented as type qualifiers: cdecl,
stdcall, __fastcall, __w64, __thread, noreturn, __malloc__, format,
__attribute, __attribute_used__, __declspec, etc.

Pre-ANSI versions of C usually #define const, restrict, or volatile to
nothing. If your C code doens't work properly without the type qualifiers,
you have a coding error. Using a type qualifier to _fix_ a problem should
be a 'red flag' that something is incorrect.


Rod Pemberton

 

[Ben Pfaff]

Type qualifiers modify the way the data is used or accessed. Many
non-standard "attributes" are implemented as type qualifiers: cdecl,
stdcall, __fastcall, __w64, __thread, noreturn, __malloc__, format,
__attribute, __attribute_used__, __declspec, etc.

In the implementations that I am familiar with, the __thread
extension is a storage class, not a type qualifier.

 

[Keith Thompson]

Pre-ANSI versions of C usually #define const, restrict, or volatile to
nothing.

No. Code intended to run on pre-ANSI C implementations may #define
them to nothing, but the implementations themselves wouldn't do so.

 

[Eric Sosman]

Type qualifiers modify the way the data is used or accessed. Many
non-standard "attributes" are implemented as type qualifiers: cdecl,
stdcall, __fastcall, __w64, __thread, noreturn, __malloc__, format,
__attribute, __attribute_used__, __declspec, etc.

Pre-ANSI versions of C usually #define const, restrict, or volatile to
nothing. If your C code doens't work properly without the type qualifiers,
you have a coding error. Using a type qualifier to _fix_ a problem should
be a 'red flag' that something is incorrect.

I'd agree for `const' and `restrict', but not for
`volatile'.

int func(void) {
jmp_buf buff;
int value = 0;
while (setjmp(buff) == 0) {
otherfunc(value++);
}
return value;
}

This code has an error, and the fix is to add `volatile'
to the declaration of `value'.