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digitalmars.D.learn - access violation error

reply Michael P. <baseball.mjp gmail.com> writes:
/* 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

adjectives
	{
		scanf( "%s", &adjectives[ i ] );
	}
	

	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!
Aug 13 2008
next sibling parent reply Wyverex <wyverex.cypher gmail.com> writes:
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

adjectives
 	{
 		scanf( "%s", &adjectives[ i ] );
 	}
 	

 	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!


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...
Aug 13 2008
parent reply "Koroskin Denis" <2korden gmail.com> writes:
On Thu, 14 Aug 2008 01:23:05 +0400, Wyverex <wyverex.cypher 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 =3D 6; //max number that user enters is 5, 6 to be=




  =


 safe 	char[][] nouns; //same as above, but for nouns
 	nouns.length =3D 6; //same as adjectives reason
 	=





 	//get adjectives first
 	for ( int i =3D 0; i < numberOfAdjectives; i++ ) //get the specified=







 of adjectives
 	{
 		scanf( "%s", &adjectives[ i ] );
 	}
 	=






 	for ( int i =3D 0; i < numberOfNouns; i++ )
 	{
 		scanf( "%s", &nouns[ i ] );
 	}
 	=





 	//print out all possible similies
 	for ( int i =3D 0; i < numberOfAdjectives; i++ )
 	{
 		for ( int j =3D 0; j < numberOfNouns; j++ )
 		{
 			//for every adjective, place a noun after and turn it into a simil=




ie

 			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 th=
is  =

pointer to a function that accepts a pointer to a preallocated buffer fo=
r  =

a string to be written to.

A quick fix would be to:
1) allocate a buffer:
nouns[i] =3D 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 shou=
ld  =

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!
Aug 13 2008
next sibling parent Wyverex <wyverex.cypher gmail.com> writes:
Koroskin Denis wrote:


 

 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!




Worked on my machine!!  Though I am using tangobos....
Aug 13 2008
prev sibling parent reply Michael P. <baseball.mjp gmail.com> writes:
Koroskin Denis Wrote:


 On Thu, 14 Aug 2008 01:23:05 +0400, Wyverex <wyverex.cypher 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

 of adjectives
 	{
 		scanf( "%s", &adjectives[ i ] );
 	}
 	

 	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...

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?
I guess I should check the documentation for some stuff like that.
Aug 13 2008
next sibling parent reply "Koroskin Denis" <2korden gmail.com> writes:
On Thu, 14 Aug 2008 04:21:05 +0400, Michael P. <baseball.mjp gmail.com> =
 =

wrote:


 Koroskin Denis Wrote:


 On Thu, 14 Aug 2008 01:23:05 +0400, Wyverex <wyverex.cypher 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 possib=








le

 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 =3D 6; //max number that user enters is 5, 6 to=








 be

 safe 	char[][] nouns; //same as above, but for nouns
 	nouns.length =3D 6; //same as adjectives reason
 	=









 	//get adjectives first
 	for ( int i =3D 0; i < numberOfAdjectives; i++ ) //get the specif=










 of adjectives
 	{
 		scanf( "%s", &adjectives[ i ] );
 	}
 	=










 	for ( int i =3D 0; i < numberOfNouns; i++ )
 	{
 		scanf( "%s", &nouns[ i ] );
 	}
 	=









 	//print out all possible similies
 	for ( int i =3D 0; i < numberOfAdjectives; i++ )
 	{
 		for ( int j =3D 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 wi=




ll  =


 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] =3D 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 u=
se.


 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.
Aug 13 2008
parent Michael P. <baseball.mjp gmail.com> writes:
 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.



Okay, thanks, I'll be using readf from now on. :D
-Michael P.
Aug 13 2008
prev sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
"Michael P." wrote

 Koroskin Denis Wrote:


 On Thu, 14 Aug 2008 01:23:05 +0400, Wyverex
 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

 of adjectives
 {
 scanf( "%s", &adjectives[ i ] );
 }


 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!


 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.  both scanf and din.readf are variadic functions (meaning, they take a 
variable number and type of arguments).  However, readf is D variadic, 
meaning that along with the addresses of all the variables you want to read, 
it also gets a TypeInfo telling the function which type each argument is. 
So it can check and make sure you are passing the right type.  In fact, I 
think %s is a catch all which means for readf to use the TypeInfo to tell 
how to scan the arguments in.

The scanf function is C variadic, and so does not have this ability.  So 
when you are passing a pointer and saying 'scan in a char*', it has to take 
your word for it that you are actually passing a char ** (even though you 
were passing a char[] *)

Note that char[] is not the same as char*.  The former is a struct with a 
char* and a length in it.  The fact that it worked in your code at all is a 
miracle :)

Glad you got it working!

-Steve
Aug 14 2008
prev sibling parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
Most likely, this is failing because you are using scanf.  Stop using it :) 
Use din.readf instead:

import std.cstream;

char[] str;
din.readf("%s", &str);

-Steve

"Michael P." <baseball.mjp gmail.com> wrote in message 
news:g7vi50$29f0$1 digitalmars.com...

 /* 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

 adjectives
 {
 scanf( "%s", &adjectives[ i ] );
 }


 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!
Aug 13 2008
parent Gide Nwawudu <gide btinternet.com> writes:
On Wed, 13 Aug 2008 17:35:42 -0400, "Steven Schveighoffer"
<schveiguy yahoo.com> wrote:


Most likely, this is failing because you are using scanf.  Stop using it :) 
Use din.readf instead:

import std.cstream;

char[] str;
din.readf("%s", &str);


The code above causes an Access Violaion in D2. The following works.

import std.stdio   : writeln;
import std.cstream : din;

int main() {
	char[] str;
	din.readf(&str);
	writeln(str);
	return 0;
}


Gide
Sep 17 2008