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digitalmars.D - Why is a variable allowed to be declared twice?

reply jicman <jicman_member pathlink.com> writes:
As in,

import std.stdio;
void main()
{
int i;
for (int i=0;i<2;i++)
writefln(i);
}

Should not have the compiler complained about it being declared twice?

I missed this one and it caused me. :-)

thanks,

josé
Mar 08 2005
parent reply brad domain.invalid writes:
jicman wrote:

 As in,
 
 import std.stdio;
 void main()
 {
 int i;
 for (int i=0;i<2;i++)
 writefln(i);
 }
 
 Should not have the compiler complained about it being declared twice?
 
 I missed this one and it caused me. :-)
 
 thanks,
 
 josé
 
 


No, the int i inside the for loop has a different scope.  This is the 
same as C++, and infact g++ doesn't even warn about i being hiding with 
-Wall on.
On a standards compilant C++ compiler (which MSVC by default is not) 
this will break
<code>
for (int i=0; i < 10; i++)
;
printf("%i\n", i);  // should be an error because i is no longer in scope.
</code>

D has the same scoping rules for "for" loops.

Brad
Mar 08 2005
next sibling parent "Matthew" <admin stlsoft.dot.dot.dot.dot.org> writes:
Most/all decent C++ compilers warn about this ...


<brad domain.invalid> wrote in message 
news:d0lrc9$12oo$1 digitaldaemon.com...

 jicman wrote:

 As in,

 import std.stdio;
 void main()
 {
 int i;
 for (int i=0;i<2;i++)
 writefln(i);
 }

 Should not have the compiler complained about it being declared 
 twice?

 I missed this one and it caused me. :-)

 thanks,

 josé


 No, the int i inside the for loop has a different scope.  This is the 
 same as C++, and infact g++ doesn't even warn about i being hiding 
 with -Wall on.
 On a standards compilant C++ compiler (which MSVC by default is not) 
 this will break
 <code>
 for (int i=0; i < 10; i++)
 ;
 printf("%i\n", i);  // should be an error because i is no longer in 
 scope.
 </code>

 D has the same scoping rules for "for" loops.

 Brad
Mar 08 2005
prev sibling parent reply Ant <duitoolkit yahoo.ca> writes:
On Wed, 09 Mar 2005 16:43:34 +1300, brad wrote:

but this looks like it shouldn't be valid
(http://www.digitalmars.com/d/statement.html#block):

import std.stdio;
void main(char[][] args)
{
	int i = 25;
	{
		int args;
	}
	{
		int i = 15;
		writefln("in ",i);
	}
	for (int i=0; i<2; i++)
	{
		writefln("for ",i);
		for (int i=425; i<427; i++)
		{
			writefln("\tfor ",i);
		}
	}
	writefln("out ",i);
}


#outputs
in 15
for 0
	for 425
	for 426
for 1
	for 425
	for 426
out 25


Ant
Mar 08 2005
parent jicman <jicman_member pathlink.com> writes:
yeah, well, I was right... :-)

Ant says...

On Wed, 09 Mar 2005 16:43:34 +1300, brad wrote:

but this looks like it shouldn't be valid
(http://www.digitalmars.com/d/statement.html#block):

import std.stdio;
void main(char[][] args)
{
	int i = 25;
	{
		int args;
	}
	{
		int i = 15;
		writefln("in ",i);
	}
	for (int i=0; i<2; i++)
	{
		writefln("for ",i);
		for (int i=425; i<427; i++)
		{
			writefln("\tfor ",i);
		}
	}
	writefln("out ",i);
}


#outputs
in 15
for 0
	for 425
	for 426
for 1
	for 425
	for 426
out 25


Ant
Mar 09 2005