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Sprintf and hex dumps

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gargg321

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Sprintf and hex dumps

Jun 20th, 2008

Hey Guys,

I am new to C programming and I got a task of storing hex dumps in character array and then use them as a string. I use the sprintf function for the job but it is giving me incorrect results. Please help me out. I am writing a prototype of the functionality I want to use.

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
#include<stdio.h>
int main()
{
	char a[25];
	int i;
	sprintf(a,"%d%d%d",0x0000001F,0x00000001,0x00271418);
	for(i=0;i<8;i++)
	{
		printf("\n%d",a[i]);
	}
	return 0;
}
#include<stdio.h>
int main()
{
	char a[25];
	int i;
	sprintf(a,"%d%d%d",0x0000001F,0x00000001,0x00271418);
	for(i=0;i<8;i++)
	{
		printf("\n%d",a[i]);
	}
	return 0;
}

Last edited by Ancient Dragon; Jun 20th, 2008 at 8:13 am. Reason: add code tags

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Re: Sprintf and hex dumps

Jun 20th, 2008

"%d" will produce decimal. If you want hex then use "%x"

Try this:

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
int main()
{
	char a[25];
	int i;
	sprintf(a,"%x%x%x",0x0000001F,0x00000001,0x00271418);
	for(i=0;i<8;i++)
	{
		printf("%c\n",a[i]);
	}
	return 0;
}
int main()
{
	char a[25];
	int i;
	sprintf(a,"%x%x%x",0x0000001F,0x00000001,0x00271418);
	for(i=0;i<8;i++)
	{
		printf("%c\n",a[i]);
	}
	return 0;
}

Last edited by Ancient Dragon; Jun 20th, 2008 at 8:20 am.

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gargg321

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Re: Sprintf and hex dumps

Jun 20th, 2008

I have tried it already. 1F should return the value 31 but instead it is returning 33. Same with all hex dumps. they all are returning incorrect results.

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niek_e

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Re: Sprintf and hex dumps

Jun 20th, 2008

Change the %x to %d with the sprintf()
use %c when printing the chars

this code:

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
int main()
{
	char a[25];
	int i;
	sprintf(a,"%d%d%d",0x0000001F,0x00000001,0x00271418);
	for(i=0;i<8;i++)
	{
		printf("%c",a[i]);
	}
	return 0;
}
int main()
{
	char a[25];
	int i;
	sprintf(a,"%d%d%d",0x0000001F,0x00000001,0x00271418);
	for(i=0;i<8;i++)
	{
		printf("%c",a[i]);
	}
	return 0;
}

works fine for me..

Last edited by niek_e; Jun 20th, 2008 at 8:40 am.

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Re: Sprintf and hex dumps

Jun 20th, 2008

sprintf() doesn't work that way. Each digit of the number will be placed in a different element of the character array. So for 0x1f the a[0] == '1' and a[1] == 'f' (assuming "%x")

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
#include<stdio.h>
int main()
{
    char a[25] = {0};
	int i;
    a[0] = 0x1f;
    a[1] = 0x01;
    a[2] = 0x00271418;
	//sprintf(a,"%4d%4d%4d",0x0000001F,0x00000001,0x00271418);
	for(i=0; i <3; i++)
	{
		printf("%d\n",a[i]);
	}
    return 0;
}
}
#include<stdio.h>
int main()
{
    char a[25] = {0};
	int i;
    a[0] = 0x1f;
    a[1] = 0x01;
    a[2] = 0x00271418;
	//sprintf(a,"%4d%4d%4d",0x0000001F,0x00000001,0x00271418);
	for(i=0; i <3; i++)
	{
		printf("%d\n",a[i]);
	}
    return 0;
}
}

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Re: Sprintf and hex dumps

Jun 20th, 2008

@AD:

But that's not what he wants right? I thought he wanted the decimal values of the hex numbers stored as a string in a char-array?
So my code should be OK

Last edited by niek_e; Jun 20th, 2008 at 8:43 am.

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Re: Sprintf and hex dumps

Jun 20th, 2008

•

Originally Posted by niek_e

Change the %x to %d with the sprintf()
use %c when printing the chars

this code:

works fine for me..

But I think he was expending a[0] to be 31.

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Re: Sprintf and hex dumps

Jun 20th, 2008

•

Originally Posted by Ancient Dragon

But I think he was expending a[0] to be 31.

Hmm. Let's ask:

@gargg321:

Do you want an array like this:
a[0] = 31
a[1] = 1
etc

or like this:
a[0] = '3'
a[1] = '1'
a[2] = '1'
etc

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Re: Sprintf and hex dumps

Jun 20th, 2008

Guys I like the array to be of first option. I think the solution given by Ancient Dragon is OK with me but he is not using the sprintf function, instead he's given every element of array indidually. The string of hex dumps I have to use is real long and giving individual values is simply not possible. When I am using sprintf the problem still persists.

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Re: Sprintf and hex dumps

#10

Jun 20th, 2008

You didn't answer Niek's question. Which way do you expect to see the data ? If you want it similiar to what I posted then you can't use sprintf(). And the way I posted, one char can only hold a value up to 127 decimal (signed integer). If the values are larger than that then you can't do it my way.

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