Programming Forums > Application Development > C

Dark Flare Knight · Jun 24th, 2006, 5:36 PM

could someone have a look at this code and tell me what's wrong here?
when i use visual studio, i get an unhandled exception, right after the program reads and prints the data from clients.dat.

(Toggle Plain Text)

#include <stdio.h>

int main (void)
{
	char *data;
	FILE *file;

	fopen_s (&file, "clients.dat", "r");

	fscanf_s (file, "%s", &data);

	fclose (file);

	printf ("%s\n", &data);

	return 0;
}

thanks.

DaWei · Jun 24th, 2006, 6:05 PM

char *data; defines a pointer to a char string. It doesn't declare the string or provide memory for it. That has to be done IN ADDITION. You can't store your girlfriend in your address book, it takes a house or apartment or something. Then you can put the pointer (address) in your book. You still need the house. See the pointer tutorial referenced in my sig. Meanwhile, declare a place for the string and either use the address of the place directly, or make a pointer to it and use that. Here's the deal: you're trying to store the whole damn string in what is, in most current systems, a 4-byte area (required for a pointer). You're most likely putting more than four bytes there and trashing memory. Quick trip off into the weeds for your system to barf. Additionally, the argument in fscanf_s needs to be a pointer to the area to store the stuff in. You currently have a pointer to a pointer. Same deal. Either of these, individually or together, are going to kill you.

Dragon_Master · Jun 24th, 2006, 6:12 PM

I was just going to say that, DaWei . DaWei's right (he always is) You would have to allocate an array for that data AND make sure it's the appropriate size... Why don't people understand pointers? I guess I understood them, thanks to the fact I learned z80 assembly before C.

grumpy · Jun 24th, 2006, 6:17 PM

Quote:

Originally Posted by Dragon_Master

DaWei's right (he always is)

Shhhh ..... don't say that, he may start to believe it.

Dragon_Master · Jun 24th, 2006, 6:20 PM

DaWei reminds me of this dude I know named Paul. Execept Paul hates all programming languages execept Ada...

DaWei · Jun 24th, 2006, 6:45 PM

Quote:

he may start to believe it

No chance. Two ex-wives, four daughters, and a ton of female friends deflate my ego if it shows signs of erupting. They're so busy with that they can't curtail my curmudgeonliness, though.

Dragon_Master · Jun 24th, 2006, 6:57 PM

So, Dawei (I tried not get off topic, but failed) what do you think about Ada?

grumpy · Jun 24th, 2006, 7:13 PM

He probably thinks Ada is a nice girl.

DaWei · Jun 24th, 2006, 7:16 PM

I was around, doing some stuff for the USPS, when it was initially decided that Ada would be THE language used in governmental projects. I can't speak for others, but in our case it meant use Ada or be effective, take your choice. We didn't use Ada. The other Ada, of course, IS a nice girl, with longer legs than Cobol.

Dragon_Master · Jun 24th, 2006, 7:27 PM

What?! Yeah, government seems to like Ada, because of it's security, but it's not used any more... Why? What do they use now?

Jun 24th, 2006, 5:36 PM	#1
Dark Flare Knight Hobbyist Programmer Join Date: Mar 2005 Location: Canada Posts: 113 Rep Power: 4	help could someone have a look at this code and tell me what's wrong here? when i use visual studio, i get an unhandled exception, right after the program reads and prints the data from clients.dat. (Toggle Plain Text) #include <stdio.h> int main (void) { char data; FILE file; fopen_s (&file, "clients.dat", "r"); fscanf_s (file, "%s", &data); fclose (file); printf ("%s\n", &data); return 0; } #include <stdio.h> int main (void) { char data; FILE file; fopen_s (&file, "clients.dat", "r"); fscanf_s (file, "%s", &data); fclose (file); printf ("%s\n", &data); return 0; } thanks.

Jun 24th, 2006, 6:05 PM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	char data; defines a pointer to a char string. It doesn't declare the string or provide memory for it. That has to be done IN ADDITION. You can't store your girlfriend in your address book, it takes a house or apartment or something. Then you can put the pointer (address) in your book. You still need the house. See the pointer tutorial referenced in my sig. Meanwhile, declare a place for the string and either use the address of the place directly, or make a pointer to it and use that. Here's the deal: you're trying to store the whole damn string in what is, in most current systems, a 4-byte area (required for a pointer). You're most likely putting more than four bytes there and trashing memory. Quick trip off into the weeds for your system to barf. Additionally, the argument in fscanf_s needs to be a pointer to the area to store the stuff in. You currently have a pointer to a pointer. Same deal. Either of these, individually or together, are going to kill you. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers*

Jun 24th, 2006, 7:16 PM	#9
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	I was around, doing some stuff for the USPS, when it was initially decided that Ada would be THE language used in governmental projects. I can't speak for others, but in our case it meant use Ada or be effective, take your choice. We didn't use Ada. The other Ada, of course, IS a nice girl, with longer legs than Cobol. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

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Jun 24th, 2006, 6:12 PM	#3
Dragon_Master Programmer Join Date: Jan 2006 Location: Some where Posts: 74 Rep Power: 3	I was just going to say that, DaWei . DaWei's right (he always is) You would have to allocate an array for that data AND make sure it's the appropriate size... Why don't people understand pointers? I guess I understood them, thanks to the fact I learned z80 assembly before C.

Jun 24th, 2006, 6:20 PM	#5
Dragon_Master Programmer Join Date: Jan 2006 Location: Some where Posts: 74 Rep Power: 3	DaWei reminds me of this dude I know named Paul. Execept Paul hates all programming languages execept Ada...

Jun 24th, 2006, 6:57 PM	#7
Dragon_Master Programmer Join Date: Jan 2006 Location: Some where Posts: 74 Rep Power: 3	So, Dawei (I tried not get off topic, but failed) what do you think about Ada?

Jun 24th, 2006, 7:13 PM	#8
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,223 Rep Power: 5	He probably thinks Ada is a nice girl.

Jun 24th, 2006, 7:27 PM	#10
Dragon_Master Programmer Join Date: Jan 2006 Location: Some where Posts: 74 Rep Power: 3	What?! Yeah, government seems to like Ada, because of it's security, but it's not used any more... Why? What do they use now?

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