Difference between const char * and char const *

explorecpp · 08-08-2008, 07:08 PM

Hi,

Can any one please explain me the difference between using a const char * or a char const *. I used both in the below program and everything worked fine except for a warning when I compiled.

Code:

int main()
{
   const char *s;   //Or char const *s;
   s = (char *) malloc (10);
   strcpy(s, "abc");
   return 0;
}

Thanks in advance!!!

tabstop · 08-08-2008, 07:12 PM

const char * and char const * both mean the same thing -- a pointer to chars that you cannot change (you can change the pointer, so the malloc is ok, but you CANNOT change the characters pointed to, so the strcpy is bad).

grumpy · 08-08-2008, 11:05 PM

The basic rule of thumb with const (and volatile) keyword is that it applies to whatever is immediately to its left. If there is nothing to its left, it applies to whatever is immediately to its right. The standard is a bit more specific in how it describes this, but comes essentially to the same thing.

By this logic, "const char *" is a (non-const) pointer to a const char, and "char const *" means the same thing.

whiteflags · 08-09-2008, 12:22 AM

FYI, the warning was probably due to casting malloc's return value.

void * malloc (size_t nbytes);

There is no reason to cast the return value of malloc in C anymore because void pointers are assignable to pointers of any type.

grumpy · 08-09-2008, 04:48 AM

Actually, the warning would be on the strcpy() call. The first argument of strcpy() is copied to, so is not a pointer to const. But you are passing a const char * as first argument .....

08-08-2008, 07:08 PM	#1
explorecpp Registered User Join Date: Aug 2008 Posts: 1	Difference between const char * and char const * Hi, Can any one please explain me the difference between using a const char * or a char const . I used both in the below program and everything worked fine except for a warning when I compiled. Code: int main() { const char s; //Or char const s; s = (char ) malloc (10); strcpy(s, "abc"); return 0; } Thanks in advance!!!
explorecpp is offline

08-08-2008, 07:12 PM	#2
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	const char * and char const * both mean the same thing -- a pointer to chars that you cannot change (you can change the pointer, so the malloc is ok, but you CANNOT change the characters pointed to, so the strcpy is bad).
tabstop is offline

08-08-2008, 11:05 PM	#3
grumpy Registered User Join Date: Jun 2005 Posts: 1,343	The basic rule of thumb with const (and volatile) keyword is that it applies to whatever is immediately to its left. If there is nothing to its left, it applies to whatever is immediately to its right. The standard is a bit more specific in how it describes this, but comes essentially to the same thing. By this logic, "const char " is a (non-const) pointer to a const char, and "char const " means the same thing.
grumpy is offline

08-09-2008, 12:22 AM	#4
whiteflags Registered User Join Date: Apr 2006 Location: United States Posts: 3,202	FYI, the warning was probably due to casting malloc's return value. void * malloc (size_t nbytes); There is no reason to cast the return value of malloc in C anymore because void pointers are assignable to pointers of any type.
whiteflags is offline

08-09-2008, 04:48 AM	#5
grumpy Registered User Join Date: Jun 2005 Posts: 1,343	Actually, the warning would be on the strcpy() call. The first argument of strcpy() is copied to, so is not a pointer to const. But you are passing a const char * as first argument .....
grumpy is offline

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