access violation error

[Koroskin Denis]

On Thu, 14 Aug 2008 04:21:05 +0400, Michael P. <baseball.mjp at gmail.com>  
wrote:

> Koroskin Denis Wrote:
>
>> On Thu, 14 Aug 2008 01:23:05 +0400, Wyverex <wyverex.cypher at gmail.com>
>> wrote:
>>
>> > Michael P. wrote:
>> >> /* junior304.d
>> >> 2008 junior problem 3
>> >> Smile with similies
>> >> Ask for 2 numbers; the number of adjectives and nouns
>> >> After you get the numbers and nouns and adjectives, out all possible
>> >> similies
>> >> August 12th, 2008 */
>> >>  //Imports
>> >> import std.stdio;
>> >>  /*****
>> >> *Main*
>> >> *****/
>> >> void main()
>> >> {
>> >> 	int numberOfAdjectives;
>> >> 	scanf( "%d", &numberOfAdjectives );
>> >> 	int numberOfNouns;
>> >> 	scanf( "%d", &numberOfNouns );
>> >> 	
>> >> 	char[][] adjectives; //array of strings to hold the adjectives
>> >> 	adjectives.length = 6; //max number that user enters is 5, 6 to be
>> >> safe 	char[][] nouns; //same as above, but for nouns
>> >> 	nouns.length = 6; //same as adjectives reason
>> >> 	
>> >> 	//get adjectives first
>> >> 	for ( int i = 0; i < numberOfAdjectives; i++ ) //get the specified #
>> >> of adjectives
>> >> 	{
>> >> 		scanf( "%s", &adjectives[ i ] );
>> >> 	}
>> >> 	
>> >> 	//now get the # of nouns specified
>> >> 	for ( int i = 0; i < numberOfNouns; i++ )
>> >> 	{
>> >> 		scanf( "%s", &nouns[ i ] );
>> >> 	}
>> >> 	
>> >> 	//print out all possible similies
>> >> 	for ( int i = 0; i < numberOfAdjectives; i++ )
>> >> 	{
>> >> 		for ( int j = 0; j < numberOfNouns; j++ )
>> >> 		{
>> >> 			//for every adjective, place a noun after and turn it into a  
>> similie
>> >> 			writefln( "%s as %s", adjectives[ i ], nouns[ j ] );
>> >> 		}
>> >> 	}
>> >> }
>> >>   I get an accessviolation when I enter the last 2 for loops; any
>> >> reason why?
>> >>  Input is:
>> >> 3
>> >> 2
>> >> Easy
>> >> Soft
>> >> Smart
>> >> pie
>> >> rock
>> >>  error!
>> >
>> Your code is seriously broken!
>>
>> The following line is wrong, for example:
>> > scanf( "%s", &nouns[ i ] );
>>
>> What are you doing here? Are you out of your mind? You are passing a
>> pointer to a char[]* to a function that accept a char*. Your array will  
>> be
>> overwritten with whatever you will type. It is wrong, wrong, wrong!
>>
>> I think that you don't understand something. First of all, what is a
>> char[]? It is a struct that consists of a array size and a pointer:
>>
>> struct CharArray {
>>     size_t size;
>>     char* ptr;
>> }
>>
>> typeof(nounts[i]) is a char[], typeof(&nouns[i]) is char[]*. You pass  
>> this
>> pointer to a function that accepts a pointer to a preallocated buffer  
>> for
>> a string to be written to.
>>
>> A quick fix would be to:
>> 1) allocate a buffer:
>> nouns[i] = new char[64];
>> 2) pass a pointer to the preallocated buffer:
>> scanf("%s", nouns[i].ptr);
>>
>> A good fix would be to use readf instead. I didn't use it, but this  
>> should
>> be sufficient:
>> readf("%s", &nouns[i]);
>>
>>
>> > quick fix is to use printf
>> > printf( "%s as %s", &adjectives[ i ], &nouns[ j ] );
>> >
>> > i think (not sure don't really use phobos that much) scanf doesn't
>> > return strings in a format writef likes...
>> >
>> > I though theres a readf but cant find documentation on it...
>>
>> Test before posting, please!
>
>
> Sorry I made you angry...
>

No, you didn't. It just proves that C functions are unsafe and hard to use.

> I changed all the scanfs to din.readfs and everything worked okay...  
> does that solve my passing a pointer to a string to function that  
> accepts a pointer to a char?

Yes, I think.

> I guess I should check the documentation for some stuff like that.

Well, you should understand what are you doing when using C library. It is  
unsafe and very error-prone.
In fact, you were doing fine, just used wrong function. Compare the  
following:

char[] buffer; scanf("%s", &buffer); vs char[] buffer; readf("%s",  
&buffer);

They are almost the same, but D version (readf) is an order of magnitude  
smarter and safer because of type-safe variadic functions.