newbee: initializing arrays

breaka · 06-12-2006, 09:46 AM

hi, how do you initialize empty (multi)dimensional arrays correctly cause i'm getting general protection errors when using arrays in a function and i think its cause i'm not initializing them.

**Dave_Sinkula** · 06-12-2006, 09:50 AM

Code:

char text[10][50] = {0};

Dante Shamest · 06-12-2006, 09:50 AM

Initialize them to what? If it's 0, you can use memset.

It also depends if your multidimensional arrays are created using [][] or using pointer-to-pointers.

It would help if you post a sample code for us to compile.

breaka · 06-12-2006, 09:54 AM

empty arrays using [],

i wrote a simple text input function (stops asking for text when hitting enter only):

here you go:

Code:

#include<stdio.h>
#include<string.h>

void input (char *);

int main (void){

	  char text[10][50]={0};       //EDIT

	  input(&text[0][0]);

return 0;
}

void input (char *p){

	  int i,sw=0;

	  for(i=0; i<10 && sw!=1; i++){

			printf("%d",p);

			scanf("%[^\n]\n",*(p+i*50));
			if (*(p+i*50)==0)
				sw=1;
	  }
}

breaka · 06-12-2006, 10:01 AM

initialisation doesnt seem to cause the general protection error, is there a way to diagnose them

**Dave_Sinkula** · 06-12-2006, 10:01 AM

Your function's signature should be like this.

Code:

int input (char p[10][50])

And you'd call it like this.

Code:

int count = input(text);

Now stop doing this.

Code:

scanf("%[^\n]\n",*(p+i*50));

And read the FAQ on string input.

breaka · 06-12-2006, 10:11 AM

well actually i'm using

Code:

scanf("%[^\n]%*c",*(p+i*50));

with %*c instead of \n but i guess thats wrong also;
i used this code to enter lines of text with interuption when hitting enter only. Guess theres a better way then. Is it the use of pointers?

checkin out the faq now

**Salem** · 06-12-2006, 10:56 AM

> void input (char *);
Is the only reason for doing this because you don't know how to pass multi-dimensional arrays to a function?

Code:

#include<stdio.h>
#include<string.h>

void input (char a[][50]);

int main (void){
  char text[10][50]={0};       //EDIT
  input(text);
  return 0;
}

void input (char p[][50]){
	  int i,sw=0;

	  for(i=0; i<10 && sw!=1; i++){
			fgets( p[i], sizeof p[i], stdin );
	  }
}

breaka · 06-12-2006, 11:10 AM

to salem: yes, i simply didn't know that (yet). i tought giving adress of first element in array was enough.
1)why only defining one dimention's length?

to dave:

Quote:

Originally Posted by Dave_Sinkula

Now stop doing this.

Code:

scanf("%[^\n]\n",*(p+i*50));

2)wich part should i stop using? fgets in stead of scanf?

3)Is there a way for newbees to diagnose general exeption errors by there numbers. when do those errors occur actually?

**Salem** · 06-12-2006, 11:16 AM

> fgets in stead of scanf?
In almost all cases, it's much simpler and safer to use fgets() to read into some temporary buffer, where you can then validate and convert the data as appropriate, before finally storing the data in it's final location.

> why only defining one dimentions length?
You have to define ALL the dimensions except for the left-most one (which is optional).

All these prototypes are equivalent.

Code:

void input (char text[10][50]);
void input (char text[][50]);
void input (char (*text)[50]);

Note that the first one is simply a copy/paste of the array you want to pass.

breaka · 06-12-2006, 11:21 AM

thank you guyz, lot a work to do here, is there a simple answer to question 3

**Dave_Sinkula** · 06-12-2006, 12:20 PM

Quote:

Originally Posted by breaka

3)Is there a way for newbees to diagnose general exeption errors by there numbers. when do those errors occur anyway?

Fix all errors and warnings in the code first so that it is 99% unlikely you encounter one.

For instance, none of these is correct.

Code:

printf("%d",p);
scanf("%[^\n]\n",*(p+i*50));
scanf("%[^\n]%*c",*(p+i*50));

Crank up the warning level; hopefully it will then point these out to you.

06-12-2006, 09:46 AM	#1
breaka Registered User Join Date: Jun 2006 Posts: 45	newbee: initializing arrays hi, how do you initialize empty (multi)dimensional arrays correctly cause i'm getting general protection errors when using arrays in a function and i think its cause i'm not initializing them.
breaka is offline

06-12-2006, 09:50 AM	#2
Dave_Sinkula Just Lurking Join Date: Oct 2002 Posts: 5,006	Code: char text[10][50] = {0}; __________________ 7. It is easier to write an incorrect program than understand a correct one. 40. There are two ways to write error-free programs; only the third one works.*
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06-12-2006, 09:50 AM	#3
Dante Shamest Even death may die... Join Date: Apr 2003 Location: Malaysia Posts: 970	Initialize them to what? If it's 0, you can use memset. It also depends if your multidimensional arrays are created using [][] or using pointer-to-pointers. It would help if you post a sample code for us to compile.
Dante Shamest is offline

06-12-2006, 09:54 AM	#4
breaka Registered User Join Date: Jun 2006 Posts: 45	empty arrays using [], i wrote a simple text input function (stops asking for text when hitting enter only): here you go: Code: #include<stdio.h> #include<string.h> void input (char ); int main (void){ char text[10][50]={0}; //EDIT input(&text[0][0]); return 0; } void input (char p){ int i,sw=0; for(i=0; i<10 && sw!=1; i++){ printf("%d",p); scanf("%[^\n]\n",(p+i50)); if ((p+i50)==0) sw=1; } } Last edited by breaka; 06-12-2006 at 10:02 AM.
breaka is offline

06-12-2006, 10:01 AM	#5
breaka Registered User Join Date: Jun 2006 Posts: 45	initialisation doesnt seem to cause the general protection error, is there a way to diagnose them
breaka is offline

06-12-2006, 10:11 AM	#7
breaka Registered User Join Date: Jun 2006 Posts: 45	well actually i'm using Code: scanf("%[^\n]%c",(p+i50)); with %c instead of \n but i guess thats wrong also; i used this code to enter lines of text with interuption when hitting enter only. Guess theres a better way then. Is it the use of pointers? checkin out the faq now
breaka is offline

06-12-2006, 10:56 AM	#8
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,710	> void input (char *); Is the only reason for doing this because you don't know how to pass multi-dimensional arrays to a function? Code: #include<stdio.h> #include<string.h> void input (char a[][50]); int main (void){ char text[10][50]={0}; //EDIT input(text); return 0; } void input (char p[][50]){ int i,sw=0; for(i=0; i<10 && sw!=1; i++){ fgets( p[i], sizeof p[i], stdin ); } } __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

06-12-2006, 11:16 AM	#10
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,710	> fgets in stead of scanf? In almost all cases, it's much simpler and safer to use fgets() to read into some temporary buffer, where you can then validate and convert the data as appropriate, before finally storing the data in it's final location. > why only defining one dimentions length? You have to define ALL the dimensions except for the left-most one (which is optional). All these prototypes are equivalent. Code: void input (char text[10][50]); void input (char text[][50]); void input (char (*text)[50]); Note that the first one is simply a copy/paste of the array you want to pass. __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

06-12-2006, 11:21 AM	#11
breaka Registered User Join Date: Jun 2006 Posts: 45	thank you guyz, lot a work to do here, is there a simple answer to question 3
breaka is offline

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