Thread: Need some help to read from a file

I am a bit lost trying to read stuff from a file which has been written before.
I want my program to open an already existing file which has my friends ‘names and numbers written like this:

friend1-7372384729
friend2-9374628202
…
The input to the program will be my friend´s name and the output after searching in the file will be his number.
I have studied these functions: fscanf, fgetc, and fgets and tried to use them but it isn’t working , I must be doing something wrong.
Here is the code: I hope it isnt as awful as I think it is

Code:

#include <stdio.h>
#include <string.h>
#define d 25


int main(){
char nom[d],*a; int i=0,n;
FILE *f;
printf("\nIntroduce your friend´s name: ");
gets(nom);
if((f=fopen("telefonos.txt","r"))==NULL) printf("\nError oppening the file");

while((i!=EOF)&&(a!=nom))   i=fscanf(f,"%s",a); 
if(i==EOF) {printf("\nIt seems you haven´t got %s number registered",nom);return 0;}
printf("\n%s number is: %d", *a, n);
fclose(f);
return 0;}

you can practice how fscanf works by writing a simple test program that declares a string "friend1-7372384729" and using sscanf on it to extract the data you are looking for. sscanf works the same way fscanf works except on a string. doing it that way gets rid of the file reading stuff that is a separate problem.

thanks for taking the time to look at it, I´ve changed a few things you told me but some things are new and I don´t really understand how they work foe example what kind of format is %[^-]
I´ve done changes but still isn´t working:

Code:

#include <stdio.h>
#include <string.h>
#define SIZE 25


int main(){
char str1[SIZE]={0},str2[SIZE]={0},n[8]={0}; int i=0,j=0;
FILE *f;
printf("\nIntroduce your friend´s name: ");
gets(str1); puts(str1);
if((f=fopen("telefonos.txt","r"))==NULL)  {printf("\nError oppening the file. The program has finished"); return 0;}
while((i!=EOF)&&((strcmp(str1, str2)) != 0))  {i=fscanf(f,"%[^-]-%s", str2[j], n[j]);
											   ++i; ++j;} 
if(i==EOF) {printf("\nIt seems you haven´t got %s number registered",str1);return 0;}
printf("\n%s number is: %d", str2, n);
fclose(f);
return 0;}

I have also tried this:

Code:

i=0; strname{0};
while (strname[i]!='-') {strname[i]=fgetc(f);++i;}
if((strcmp(a, nom)) != 0)
{
  j=0; strnumber={0};
  while(strnumber[j]!='\n'){strnumber[j]=fgetc(f);++j;}
}

but I think that has to be done for every line in the file but I don´t know how to express that in C.
Anyway I´ll be glad if you can keep on helping me

Originally Posted by hk_mp5kpdw

Oh man, your code is horrendous to look at. It's very difficult to see what's going on with everything squashed together. Can you format it a bit better? You'd get more people willing to help out if you did so.

Quite true.

Code:

#include <stdio.h>
#include <string.h>
#define SIZE 25


int main(){
char str1[SIZE]={0},str2[SIZE]={0},n[8]={0}; 
int i=0,j=0;
FILE *f;


printf("\nIntroduce your friend´s name: ");
gets(str1);


if((f=fopen("telefonos.txt","r"))==NULL) 
{
    printf("\nError oppening the file. The program has finished");
	return 0;
}
   
   /*This loop is where the problem must be*/
while((i!=EOF)&&((strcmp(str1, str2)) != 0))  
{
   i=fscanf(f,"%[^-]-%s", str2[j], n[j]);
   ++i;
   ++j;
} 


if(i==EOF)
{
   printf("\nIt seems you haven´t got %s number registered",str1);
   return 0;
}
printf("\n%s number is: %s", str2, n);
fclose(f);
return 0;}

1. %[^-] means 'match any characters except a '-' but that will copy the first field, which in your example is a name, to str2. fscanf and sscanf copy the data in order of the field specs.
2. 'n' need to have enough room for the entire number and a zero delimiter. right now you only have room for 8 characters in 'n'.

try this

Code:

#include <stdio.h>
#include <stdlib.h>


int main()
{
        const char *s = "friend1-7372384729";
        char a[32];
        char b[11];
        sscanf(s,"%[^-]-%s",a,b);
        printf("%s %s\n",a,b);
    return 0;
}

Thanks to all of you. After playing around a bit with dmh2000 example I started to undestand how it works, but I think there still is a problem when I use this:

Code:

while((i!=EOF) && ((strcmp(str1, str2)) != 0))  
{
        i=fscanf(f,"%[^-]-%s",str2,n);
        printf("In str2:%s   In n:%s\n",str2,n);
}

the problem is that for the all my friend´s names except the first, str2 is reading and saving in str[0] a '\n' character that makes it jump a line and makes the strcmp(str1,str2) not work.
So after tried a few things I thought of this, that works but it isn´t very elegant:

Code:

while((i!=EOF) && ((strcmp(str1, str2)) != 0))  
{
        i=fscanf(f,"%[^-]-%s",str2,n);
        if(c>=1)
                { 
                   for(j=1;j<strlen(str2);++j) str2[j-1]=str2[j];
                  str2[strlen(str2)-1]='\0';
                }
        printf("In str2:%s   In n:%s\n",str2,n);
        c=c+1;
}

does anyone know an easier way to make str2 so as not to read a '\n' character ?

Instead of

Code:

 i = fscanf(f, "%[^-]-%s", str2, n);

use

Code:

i = fscanf(f, " %[^-]-%s", str2, n);

Note the space before the first % in the format string. %[ (and also %c and %n) doesn't skip whitespace before the input item and so you have to explicitly add it.

Bye, Andreas