Wrong output for reading data from file into program - c

Question

I've been working on a program to read data from file into a program and print it:
Here is my code:
#include <stdio.h>
#include <stdlib.h>
int main()
{
char *p;
int e;
float f;
static char a[50];
FILE *fp;
fp = fopen("new_input.txt", "r");
if (fp == NULL)
exit(0);
while (1)
{
p = fgets(a, 50, fp);
if (p == NULL)
break;
printf("%s", a);
printf("\n");
fscanf(fp, "%d", &e);
printf("%d", e);
printf("\n");
fscanf(fp, "%f", &f);
printf("%f", f);
printf("\n");
}
fclose(fp);
return 0;
}
Contents of file new_input.txt are:
Girik
12
19.98
Nikhil
13
90.89
On running on OnlineGdb however I get the following output:
Girik
12
19.980000
12
19.980000
khil
13
90.889999
Can someone explain the problem with my code?
I'm concerned about incomplete name "Nikhil" in output and printing of the value 12 and 19.99 twice.
Link to code:
https://onlinegdb.com/r1ufoP8-d

Answer 1

The problem arises because the last fscanf does not parse the \n, so when the cycle restarts the fgets will parse it and print it, naturally the next fscanf is not able to parse the string ("Nikhil", which was not parsed), because it expects an int, it's downhill from there, as the values are not parsed, what's printed is the old values of e and f from the previous cycle.
If you change your last fscanf so it parses the \n everything works fine:
Live demo
while (1)
{
p = fgets(a, 50, fp);
if (p == NULL)
break;
printf("%s", a);
fscanf(fp, "%d", &e);
printf("%d", e);
printf("\n");
fscanf(fp, "%f\n", &f); //<--here
printf("%.2f", f);//.2f specifier so it prints only 2 decimal places
printf("\n");
}
The pointer is also unnecessary you can use fgets itself as a condition i.e.:
while (fgets(a, sizeof a, fp)) //will read until the end of the file
{
printf("%s", a);
//... same code
}
Anyway, here is a version you can use that will render you the expected result and output, and, I would argue, is better:
Live demo
#include <stdio.h>
#include <stdlib.h>
int main()
{
int e;
float f;
static char a[50];
FILE *fp;
fp = fopen("new_input.txt", "r");
if (fp == NULL){
return EXIT_FAILURE;
}
// will parse until \n or 49 characters max (given the container size)
while (fscanf(fp, " %49[^\n]", a) > 0)
// ^ space - will discard any blank characters
{
printf("%s\n", a);
if(fscanf(fp, "%d", &e) > 0){
printf("%d\n", e);
}
if(fscanf(fp, "%f", &f) > 0){
printf("%.2f\n", f);
}
}
fclose(fp);
return EXIT_SUCCESS;
}
I also added the checks for the fscanf returns which is always a good practise.
Or even:
//...
while (fscanf(fp, " %49[^\n]%d%f", a, &e, &f) == 3)
{
printf("%s\n%d\n%.2f\n", a, e, f);
}
//...
However, the best solution, I believe, is to parse everything with fgets and convert the values with sscanf or strtol/strtof, it's a more robust option. Give it a try.

Answer 2

For "read data from file into a program and print it", you can use e.g. fgets or fscanf. Both uses are included in the following adaption of your example:
#include <stdio.h>
#include <stdlib.h>
int main()
{
char *p;
int e;
float f;
static char a[50];
FILE *fp;
// use fgets
printf("\nVersion with using fgets\n\n");
fp = fopen("new_input.txt", "r");
if (fp == NULL) exit(0);
while(fgets(a, 50, fp)!=NULL)
{
printf("%s", a);
}
fclose(fp);
// use fscanf
printf("\nVersion with using fscanf\n\n");
fp = fopen("new_input.txt", "r");
if (fp == NULL) exit(0);
while(fscanf(fp,"%s\n",a)!=EOF)
{
printf("%s\n", a);
}
fclose(fp);
return 0;
}
COMMENTS:
Size of a[50] needs to be larger than maximum line size.
You can also fscanf for numbers (if you are sure, that it is a number).
Check, if string is integer or float (locale) is a new topic.
Another option: With the assumption that you can rely on the format in "new_input.txt" (to account for the comment of Devolus).
#include <stdio.h>
#include <stdlib.h>
int main()
{
char *p;
int g;
float f;
static char a[50];
FILE *fp;
fp = fopen("new_input.txt", "r");
if (fp == NULL) exit(0);
while(fscanf(fp,"%s\n",a)!=EOF){
printf("%s\n", a);
fscanf(fp,"%d\n",&g);
printf("%d\n", g);
fscanf(fp,"%f\n",&f);
printf("%f\n", f);
}
fclose(fp);
return 0;
}