Question regarding const property of sizeof

[somenath]

Hi All,

The sizeof operator is evaluated at compile time .so it can be treated
as compile time constant expression.

But when I compile the following program in g++
#include<stdio.h>
int main (void)
{
size_t size = sizeof(int);
int ar[size]={0} ;
return 0;
}
I get the error

$ g++ size_of_test.cpp
size_of_test.cpp: In function `int main()':
size_of_test.cpp:5: error: variable-sized object `ar' may not be
initialized

Why it says ar is variable sized object?

But when I compile the following program it compiles with out error

#include<stdio.h>
int main (void)
{
size_t size = sizeof(int);
int ar[4]={0} ;
return 0;
}

Regards,
Somenath

 

[Sana]

Hi All,

The sizeof operator is evaluated at compile time .so it can be treated
as compile time constant expression.

But when I compile the following program in g++
#include<stdio.h>
int main (void)
{
        size_t size = sizeof(int);
        int ar[size]={0} ;
        return 0;}

in your code the variable 'size' isn't constant. try

size_t const size = sizeof(int);

 

[SG]

Hi All,

The sizeof operator is evaluated at compile time .so it can be treated
as compile time constant expression.

But when I compile the following program in g++
#include<stdio.h>
int main (void)
{
        size_t size = sizeof(int);
        int ar[size]={0} ;
        return 0;}

You need to make 'size' const:

int main (void)
{
const size_t size = sizeof(int);
int ar[size]={0} ;
return 0;
}

Cheers!
SG

 

[zhangyw80]

Hi All,

The sizeof operator is evaluated at compile time .so it can be treated
as compile time constant expression.

But when I compile the following program in g++
#include<stdio.h>
int main (void)
{
size_t size = sizeof(int);
int ar[size]={0} ;
return 0;}

You need to make 'size' const:

int main (void)
{
const size_t size = sizeof(int);
int ar[size]={0} ;
return 0;
}

Cheers!
SG

using the following code directly is ok too:
int ar[sizeof(int)] = {0};

 

[zhangyw80]

Hi All,

The sizeof operator is evaluated at compile time .so it can be treated
as compile time constant expression.

But when I compile the following program in g++
#include<stdio.h>
int main (void)
{
size_t size = sizeof(int);
int ar[size]={0} ;
return 0;}

You need to make 'size' const:

int main (void)
{
const size_t size = sizeof(int);
int ar[size]={0} ;
return 0;
}

Cheers!
SG

using the following code directly is ok too:
int ar[sizeof(int)] = {0};
of course, readability is no so good

 

[Juha Nieminen]

int main (void)
{
const size_t size = sizeof(int);
int ar[size]={0} ;
return 0;
}

Btw, out of curiosity: What is the official type returned by sizeof?