Thread: Reading a file (one double number in each line)

Dear all,

I need to read a file which has unknown number of lines, but each line is just 1 double number. How I can do that?

Please help

Thanks

Welllll... you could put on your glasses, make a nice cup of coffee and sit to do a little reading.

Or... you could get started on it, get the project as far as you can... then post your code and ask specific questions.

As tater said, you have to post an attempt. Look into fscanf. It's a little complicated, but the format specifier you want is f.

More like %lf

Oops! You're right of course nonoob.
Note to the OP: that's a lowercase L in front of the f: %lf

Originally Posted by CommonTater

Welllll... you could put on your glasses, make a nice cup of coffee and sit to do a little reading.

Or... you could get started on it, get the project as far as you can... then post your code and ask specific questions.

You are right! I should post my code first. Here is my unworking code. In the code, I assume there is less than 100 double values.

Code:

#include <stdio.h>
#include <math.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>


int main(int argc, char *argv[])
{

    FILE *file1 = fopen( argv[1], "r" );



    if ( argc !=2 ) /* argc should be 5 for correct execution */
    {
        printf( "Error of input argument number" );
    }

    int i;
    double bb;
    for (i=1;i<100;i++){
        fscanf(file1, "%f",bb);
        printf("%f",bb);
    }
}

You need to use the address operator '&'

Code:

fscanf(file1, "%lf", &bb);

You need to ensure that the file has been opened after the fopen.

If "argc should be 5 for correct execution" then wy are you testing it against 2?

Your loop control assumes that there are going to be exactly 99 doubles in the file. What if there are less? You need to test fscanf for a return value of 1. If it returns something else, exit the loop.

These two have already been mentioned:

You need to use "%lf" as the format specifier for a double.

You need to pass the address of bb, not its value. So use &bb.

Originally Posted by MK27

"f" indicates a double or a float, "lf" is undefined behaviour, "Lf" is a long double).

Are you sure it's undefined, my man page here (BSD) says that the "l" modifier is ignored for "f", same behavior as without it.

Originally Posted by printf manpage

The following length modifier is valid for the a, A, e, E, f, F, g, or G conversion:

Modifier a, A, e, E, f, F, g, G
l (ell) double (ignored, same behavior as without it)
L long double

Originally Posted by nonoob

You need to use the address operator '&'

Code:

fscanf(file1, "%lf", &bb);

Thanks, I updated my code, but there is another problem. Since I assume that the length is 100 in the file. I created a text file which only have 3 double values, but my program repeat the last value for many times (I guest 98 times). How I can solve it? The following is the new code.

Code:

#include <stdio.h>
#include <math.h>
#include <sys/types.h>
#include <sys/stat.h>


int main(int argc, char *argv[])
{

    int i;
    double bb;

    FILE *file1 = fopen( argv[1], "r" );



    if ( argc !=2 ) /* argc should be 2 for correct execution */
    {
        printf( "Error of input argument number" );
    }



    for (i=1;i<100;i++){
        fscanf(file1, "%lf",&bb);
        printf("%f",bb);
    }
}

Originally Posted by zmarcoz

Thanks, I updated my code, but there is another problem. Since I assume that the length is 100 in the file. I created a text file which only have 3 double values, but my program repeat the last value for many times (I guest 98 times). How I can solve it?

You solve it by more carefully reading the previous responses people gave you. In particular, oogabooga's response in post #9 about checking the return value of fscanf.

Originally Posted by anduril462

You solve it by more carefully reading the previous responses people gave you. In particular, oogabooga's response in post #9 about checking the return value of fscanf.

Good blame. Solved .............