Thread: size_t in source code of strlen

Hi! I read the source code of strlen() function in a book called "The Standard C Library" and it is as follows:

Code:

/* strlen function */ 
#include <string.h> 
size_t (strlen)(const char *s) 
{ /* find length of s[] */ 
const char *sc; 
for (sc = s; *sc != '\0'; ++sc) 
{ 
return (sc - s) ; 
}

What is size_t here?

unsigned int

Is it a reserved identifier?

it is an int that can not be negative.Since this is strlen which calculates the length of a string the value the function returns can not be negative.

What is a reserved identifier?

I presume it is a keyword,globally used only by the compiler

unsigned int

No, it is not necessarily an unsigned int.

7.19 Common definitions <stddef.h>
1
The header <stddef.h> defines the following macros and declares the following types.
Some are also defined in other headers, as noted in their respective subclauses.
2
The types are
ptrdiff_t
which is the signed integer type of the result of subtracting two pointers;
size_t
which is the unsigned integer type of the result of the sizeof operator;

6.5.3.4 The sizeof and _Alignof operators
Constraints

5
The value of the result of both operators is implementation-defined, and its type (an
unsigned integer type) is size_t, defined in <stddef.h> (and other headers).

So it could be any unsigned integer type. Don't assume any exact size. If the function uses size_t then you should use size_t for your variable's type.

I presume it is a keyword,globally used only by the compiler

No, it is a type of variable, just like int is a type of variable.

Jim

size_t is a typedef in stddef.h.

That's what i wanted to know..Thanks a lot guys

I did not know the above! However in this example it is certaintly an unsigned int

However in this example it is certaintly an unsigned int

Why? It could be an unsigned long on some systems, don't assume. Just because your compiler is using unsigned int for size_t doesn't mean every other compiler does. The standard leaves it to the compiler to determine the actual 'size'.

Jim

Correct.It is resolved at compilation time.You are tottaly right!