Need help with sscanf

**dgs414** · 08-08-2005

I can get the following code to error out when I put anything other than a number first, but if I input numbers first followed by a char it won't error out. For example: f431 causes an error but 431f will not. Should I attempt to use fscanf and if I should, how would I go about doing so/

Code:

#include <stdio.h> 
 

int check(char *line);
char line[MAXLINE];
int error, n, digit;
int i = 0;
int flag = 0;


void main(){ 
	
	do{
	         printf("Input a positive integer: ");
	         if (fgets(line, MAXLINE, stdin) != NULL){
	         digit = check(&line[0]);
	         error = ((sscanf(line," %d", &n) != 1 || n <= 0) && (digit == 1));  
		}
		if (error)
			printf("\nERROR: Do it again .\n");
		else 
			printf("There was no error!");
	}while (error);
}


int check(char *line){ 
	while((i < MAXLINE) && (flag == 0)){
		if (isalpha((int)line[i]))
	      flag = 1;
	    ++i;
	}
	if (flag == 0)
		return 0;
	else
		return 1;
}

**Dave_Sinkula** · 08-08-2005

How about strtol?
http://home.att.net/~jackklein/c/code/strtol.html

**quzah** · 08-08-2005

Originally Posted by dgs414

void main(){

Where ever you learned that was incorrect in its teaching. The main function always returns an int. There's a FAQ entry on it if you need more information on why it's wrong and the correct way to do it.

Quzah.

**exvor** · 08-08-2005

wow talk about unreadablity

the whold error thing is messin me up

what is your while statement checking for?

ill continue to try and understand what you were doin here but if i
cannot understand your intentions here then i cannot help. Sorry
if im sounding harsh but maybe it would help if you added comments.

**exvor** · 08-08-2005

ok i think i have it tracked down here

Code:

 
error = ((sscanf(line," %d", &n) != 1 || n <= 0) && (digit == 1));

this error checking will not work if both a letter and a number are enterd in whatever combination.

sscanf does not return 0 on false and 1 on true it returns the number of varibles found so in essence its always true as long is there is input.

**itsme86** · 08-08-2005

Originally Posted by exvor

sscanf does not return 0 on false and 1 on true it returns the number of varibles found so in essence its always true as long is there is input.

That's not true. Look at the following.

Code:

itsme@itsme:~/C$ cat sscanfexample.c
#include <stdio.h>

int main(void)
{
  int rv;
  int n;

  rv = sscanf("c1", "%d", &n);
  printf("%d\n", rv);
  rv = sscanf("1c", "%d", &n);
  printf("%d\n", rv);

  return 0;
}

Code:

itsme@itsme:~/C$ ./sscanfexample
0
1
itsme@itsme:~/C$

**quzah** · 08-09-2005

Originally Posted by exvor

sscanf does not return 0 on false and 1 on true it returns the number of varibles found so in essence its always true as long is there is input.

Actually, it returns the number of assignments. To quote the man page:

These functions return the number of input items assigned, which can be
fewer than provided for, or even zero, in the event of a matching fail-
ure. Zero indicates that, while there was input available, no conver-
sions were assigned; typically this is due to an invalid input charac-
ter, such as an alphabetic character for a `%d' conversion. The value
EOF is returned if an input failure occurs before any conversion such
as an end-of-file occurs. If an error or end-of-file occurs after con-
version has begun, the number of conversions which were successfully
completed is returned.

Quzah.

**Dave_Sinkula** · 08-10-2005

Originally Posted by dgs414

I can get the following code to error out when I put anything other than a number first, but if I input numbers first followed by a char it won't error out. For example: f431 causes an error but 431f will not. Should I attempt to use fscanf and if I should, how would I go about doing so/

Read a Number from the User, Part 2

**exvor** · 08-13-2005

Sorry man page is kinda clusterd with scanf and sscanf and fscanf

so I just checked it real fast. when i replied as to what is wrong
in the above code im not sure yet as I couldent find this post
on the message board for awhile ?

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