Thread: char pointer length problem

Hi All,

I am trying to get the length of an char pointer but the app is getting crashed by giving error - Access Violation. I am not getting why this is happening. The piece of code is given below -

CODE

Code:

int length = 0;
char** strArr = (char**)malloc(sizeof (char * )*(4));
temp=(char*)malloc(sizeof(char*)*100);

tempChar="HELLO";
strArr[0] = (char*)malloc(sizeof(char*)*(strlen(tempChar)+1)); 
strcpy(strArr[0],tempChar);

tempChar="HELLO1";
strArr[1] = (char*)malloc(sizeof(char*)*(strlen(tempChar)+1)); 
strcpy(strArr[1],tempChar);

tempChar="HELLO2";
strArr[2] = (char*)malloc(sizeof(char*)*(strlen(tempChar)+1)); 
strcpy(strArr[2],tempChar);

tempChar="HELLO3";
strArr[3] = (char*)malloc(sizeof(char*)*(strlen(tempChar)+1)); 
strcpy(strArr[3],tempChar);

length = get2DArrayLength(strArr);

int get2DArrayLength(char** charArray)
{
int len=0;
char **ptr;
for(ptr=charArray;ptr!='\0';*ptr++)
{
print("0..%s",*ptr);
if(*ptr==NULL)
break;
if(strlen(*ptr)!=0)
{
len+=strlen(*ptr);
}
print("1..%s",*ptr);
}
return len;
}

OUTPUT ::

0..HELLO
1..HELLO
0..HELLO1
1..HELLO1
0..HELLO2
1..HELLO2
0..HELLO3
1..HELLO3
segmentation fault

Please check the code and tell me what I am doing wrong in this..

thanks.

Originally Posted by Salem

1. Read the FAQ on casting malloc. In C, it isn't necessary.
2. Learn the value of indented code. I don't know whether you see indented code in your IDE, but when you posted it, it was lost. This is a real turn off.

If get2DArrayLength() is somehow trying to determine that there are 4 strings stored, then it can't.

In the same way that a char array stores a \0 to mark the end of the array (for say strlen to work), you need to store a NULL pointer at the end of your char* array to mark the end of that array.

So you would malloc 5 pointers to begin with, and set
strArr[4] = NULL;

Hi Salem,

Thanx for the reply,

Actually I am doing all this in BREW,
I have to calculate the length dynamically as I am allocating the pointer runtime and deallocating also runtime as if I will use char** then I have to use one integer to keep track of size of the first diamention. so for each char** I have to use different integers. I don't want to do use such manual solution.

I had also used this before -

So you would malloc 5 pointers to begin with, and set
strArr[4] = NULL;

but still the problem was there.


So please tell me is there any other way out for this

Thanx

Originally Posted by Salem

Well your function also needs to be fixed.

int len = 0;
while ( p[len] != NULL ) len++;
return len;

Is all you need, if p is your char** parameter in the function.

Hi,

Just have a look at this -

Code:

#include <iostream>
#include <stdio.h>

using namespace std;

void main()
{
    char ** xyz;
    int len=0,bh=0,i=0;
    cin>>len>>bh;
    xyz = (char **)malloc(sizeof(char *)*len);
	memset(xyz,NULL,(sizeof(char *)*len));
    for(i=0;i<len;i++)
    {
        xyz[i] = (char*)malloc(sizeof(char)*bh);
//		memset(xyz[i],NULL,(sizeof(char)*bh));
    }
    for(i=0; i<len;i++)
    {
        cin>>xyz[i];
        cout<<strlen(xyz[i])<<endl;
    }
    char **ptr = xyz;
    cout<<"now data count is "<<endl;
    len = 0;
	while(ptr[len]!=NULL) len++;

   /* for(ptr = xyz; ptr != '\0' ;*ptr++)
    {
        if(*ptr==NULL)
           break;
        if(strlen(*ptr) != 0)
        {
                len += strlen(*ptr);
                cout<<strlen(*ptr)<<endl;
        }
    }*/
    cout<<"Total length is "<<len<<endl;
}

it's working but it's not giving exact length of char**

Thanx

found solution -

have a look at this -

Code:

#include <iostream>
#include <stdio.h>

using namespace std;

int get2DArrayLength(char** ptr);
int main()
{
    char** xyz;
    int len=0,bh=0,i=0;
    cin>>len>>bh;
    xyz = (char**)malloc(sizeof(char*)*(len+1));
	memset(xyz,NULL,(sizeof(char*)*(len+1)));
    for(i=0;i<len;i++)
    {
        xyz[i] = (char*)malloc(sizeof(char)*bh);
		memset(xyz[i],NULL,(sizeof(char)*bh));
    }
    for(i=0; i<len;i++)
    {
        cin>>xyz[i];
        cout<<strlen(xyz[i])<<endl;
    }
	cout<<"Total length is "<<get2DArrayLength(xyz)<<endl;
}

int get2DArrayLength(char** ptr){
	int len = 0;
	while(ptr[len]!=NULL){
		cout<<"STRING  :: "<<ptr[len]<<endl;
		len++;
	}
	return len;
}

thanx

Originally Posted by vart

you should decide what language you are using
currently - you have a horrible mix of C/C++

Hi Vart,

sorry to say but does this thing matters here?
the main goal of this post is getting length of char**
rest of the thing is only for display purpose.

So please check for the solution and leave the other part.

Thanx

Ok Salem,

I'll take care of the same in the future!

Thanx