CODEWITHSUNDEEP
cformatscanf
user2745075
user2745075

Reputation:

read the header of a .pgm image file

I am attempting to read the size values from the header of a .pgm image file (mars.pgm), and assign the resulting values to the integer variables u and v using sscanf.

When executed the program prints P5 832 700 127 in the first line, which is correct (the 832 and 700 are the size values that I want to pick out).

In the second line that is meant to print u and v variables two very large numbers are printed, instead of the 832 and 700 values.

I cannot figure out why this is not working as desired. When using the small test program (located at the bottom of the post) sscanf picks out the values from a string like I expected it to.

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

int main()
{
FILE *fin;
fin= fopen ("mars.pgm","r+");
if (fin == NULL)
{
printf ("ERROR");
fclose(fin);
}


int u,v,i,d,c;
char test[20];

for (i=0; i<=20; i++)
{
test[i]=getc(fin);  
}

sscanf(test,"%d,%d,%d,%d",&c,&u,&v,&d);

printf("%s\n",test);

printf("%d  %d",u, v);


fclose(fin);
}

small test Program

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void main(void)
{
int a;
char s[3];
s[0]='1';
s[1]=' ';
s[2]='2';

sscanf(s,"%d",&a);
printf("%d",a);
}

Upvotes: 1

Views: 1747

Answers (1)

Mauren
Mauren

Reputation: 1975

First of all, I advise you to make a small test: initialize your variables with a 0, for instance, and verify what value they are holding after read operation.

Then, try removing , characters from your format string. Check if it works then.

This behavior you see is happening because fscanf() and derivatives match the full pattern when scanning, which means if your source data has no commas and your format has commas, it may be ignored.

Upvotes: 2

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