Read numbers from first N file of file

Question

I have a text file with one number in each line.

I want to read a specific number of lines from this file , lets say the first 20, what is the way to do it?

I have the following piece of code.

FILE *ft;
ft=fopen(filename,"r");
for(int k=1; k<Nt+1; k=k+1) 
{
    fscanf(ft,"%lf\n",&curve3[k]);
    printf("%lf\n",curve2[k]);
}

EDIT: I changed my code to

FILE *ft;
ft=fopen(filename,"r");
int k=1;

while(!feof(ft))
{
    if(k<=Nt)
    {
        fscanf(ft,"%lf\n",&curve2[k]);
        //printf("%lf\n",curve2[k]);
    } 
    k=k+1;
}

It still doesn't seem to work.

possible duplicate of http://stackoverflow.com/questions/3501338/c-read-file-line-by-line — Andreas DM, Jun 11 '15 at 22:39
Curious: what programing language did you study before C? Note: In C, array indexes start with 0, not 1. — chux - Reinstate Monica, Jun 11 '15 at 22:57
@chux: Ada and Pascal allow for arbitrary indexes. But their users tend to format their source code better. — too honest for this site, Jun 11 '15 at 23:03
@chux: if i initialize my counter to 1 and start puting data to array, is the same but i'm losing the first 0 place of the array??? — giorgos_stefos, Jun 11 '15 at 23:18
@George Stefos If code does not use `curve2[0]`, that element is not necessarily "lost". It is simple unused. The concern is that if the array is declared `double curve3[Nt]`, then `for (int k=1; k — chux - Reinstate Monica, Jun 12 '15 at 00:19
@George Stefos Check the return value of `fscanf(ft,"%lf\n",&curve2[k]);` before using `&curve2[k]`. — chux - Reinstate Monica, Jun 12 '15 at 00:21

score 0 · Answer 1 · answered Jun 11 '15 at 22:40

0

With this code you can read a file line by line and hence read a specific line from the text file. So, you can modify the code.

lineNumber = x;

static const char filename[] = "file.txt";
FILE *file = fopen(filename, "r");
int count = 0;
if ( file != NULL )
{
    char line[256]; /* or other suitable maximum line size */
    while (fgets(line, sizeof line, file) != NULL) /* read a line */
    {
        if (count == lineNumber)
        {
            //use line or in a function return it
            //in case of a return first close the file with "fclose(file);"
        }
        else
        {
            count++;
        }
    }
    fclose(file);
}
else
{
    //file doesn't exist
}

answered Jun 11 '15 at 22:40

Soner from The Ottoman Empire

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Minor: Why `static` in `static const char filename[]...`? – chux - Reinstate Monica Jun 12 '15 at 00:24
To do not lose their value between function calls. If it is wrong, could you illuminate with your wide experience ? @chux – Soner from The Ottoman Empire Jun 12 '15 at 00:33
Hmmm, is this code is part of a function, then `const char filename[] = "file.txt"` is sufficient as that will set `filename[]` on each function call. Your approach is not _wrong_. Just different form my experience. IAC, this query is only a minor aspect of this post. – chux - Reinstate Monica Jun 12 '15 at 02:18

Read numbers from first N file of file

1 Answers1