reading data from a file

[jj_76]

Hello,
I have the following code and I try to read data from a file. But all I
get are zero's. Any help is appreciated.
--------------------------------
#include <stdio.h>
#include <math.h>
main()
{
double mtot;
FILE *fp1;
FILE *fp2;

fp1=fopen("initial_birth","r");

while(!feof(fp1))
{
fscanf(fp1,"%f",&mtot);
printf("%f\n",mtot);
}
fclose(fp1);
fclose(fp2);
}
-----------------------

 

[Tom St Denis]

--------------------------------
#include <stdio.h>
#include <math.h>
main()
Wrong.

double mtot;
FILE *fp1;
FILE *fp2;

fp1=fopen("initial_birth","r");

Check the return value.

while(!feof(fp1))
{
fscanf(fp1,"%f",&mtot);

Check the return value, also how are you handling whitespace?

fclose(fp2);

You never opened fp2, this is wrong.

I hate *scanf functions. They're basically begging for beginners to
abuse them. arrg...

Tom

 

[Richard Heathfield]

Tom St Denis said:

Wrong.

No, it's not wrong. It's valid K&R C, and it's valid C90. It's not good
style, and it's not terribly wise, but it's not actually wrong.

Check the return value, also how are you handling whitespace?

He's also misusing feof.

I hate *scanf functions. They're basically begging for beginners to
abuse them. arrg...

Yes, it is a source of wonder to me that C teachers (and C books) introduce
such a difficult function so early.

 

[Default User]

Hello,
I have the following code and I try to read data from a file. But all
I get are zero's. Any help is appreciated.
--------------------------------
#include <stdio.h>
#include <math.h>
main()
{
double mtot;
FILE *fp1;
FILE *fp2;

fp1=fopen("initial_birth","r");

while(!feof(fp1))
{
fscanf(fp1,"%f",&mtot);
printf("%f\n",mtot);
}
fclose(fp1);
fclose(fp2);
}

This may cover the problem:

<http://c-faq.com/stdio/scanf2.html>




Brian

 

[Ronald Bruck]

Hello,
I have the following code and I try to read data from a file. But all I
get are zero's. Any help is appreciated.
--------------------------------
#include <stdio.h>
#include <math.h>
main()
{
double mtot;
FILE *fp1;
FILE *fp2;

fp1=fopen("initial_birth","r");

while(!feof(fp1))
{
fscanf(fp1,"%f",&mtot);
printf("%f\n",mtot);
}
fclose(fp1);
fclose(fp2);
}

You're closing fp2 when you never opened it; but I understand what you
mean, you probably modified the original code to use printf instead of
fprintf, remembered to remove the "fopen" but forgot to remove the
"fclose". (The mind-reader is now OUT.)

You're trying to read a double value (mtot) using a float format
specifier; use "%lf" instead of "%f".

 

[Keith Thompson]

I have the following code and I try to read data from a file. But all I
get are zero's. Any help is appreciated.

main()

int main(void)

{
double mtot;
FILE *fp1;
FILE *fp2;

fp1=fopen("initial_birth","r");

Always check the result of fopen().

while(!feof(fp1))

Don't use feof(); it doesn't do what you think it does.

{
fscanf(fp1,"%f",&mtot);

Always check the result of fscanf(). Also, you're using the wrong
format.

printf("%f\n",mtot);
}
fclose(fp1);
fclose(fp2);

You never opened fp2.

Add "return 0;" here.

}

Read section 12 of the comp.lang.c FAQ, <http://c-faq.com/>. Then
read the other sections.

As a matter of style, I always put a space after each comma, and I
usually put spaces around operators. Also, a consistent indentation
style is important. Ignoring the actual errors, here's how I would
have formatted your code:

#include <stdio.h>
#include <math.h>
main()
{
double mtot;
FILE *fp1;
FILE *fp2;

fp1 = fopen("initial_birth", "r");

while (! feof(fp1)) {
fscanf(fp1, "%f", &mtot);
printf("%f\n", mtot);
}

fclose(fp1);
fclose(fp2);
}

This is still wrong, but it's easier to read.

If you prefer to put your '{' characters by themselves on the
beginning of the next line, that's ok too.

 

[Old Wolf]

As a matter of style, I always put a space after each comma, and I
usually put spaces around operators. Also, a consistent indentation
style is important. Ignoring the actual errors, here's how I would
have formatted your code:

while (! feof(fp1)) {

For me, the ! gets lost in the ( with this style; I prefer

while ( !feof(fp1) )

But I use a syntax-highlighting editor so the ! now doesn't
get lost in the feof. My colleague has a macro which is
very readable:

while ( NOT feof(fp1) )

and doesn't take long to learn if you haven't seen it before.

NB. This is all subjective opinion of course.

 

[jj_76]

I hate *scanf functions. They're basically begging for beginners to

 

[Richard Heathfield]

jj_76 said:

Read the data as a string using fgets (or whatever), and convert it yourself
if you need to after you've got it into memory, using strtol or strtoul or
strtod or whatever.

 

[CBFalconer]

pardon my ignorance, but what is the alternative ?

Please don't delete attribution lines for quoted material.

One alternative are the routines I have published in:

<http://cbfalconer.home.att.net/download/txtio.zip>