How do I change my function so that the entire header can be parsed into the new file?

Question

So I created a function is able to pull the header from a file and put it into a new file without the comments. All the .ppm files have a max color value of 255 so here is my function:

void headerinfo(FILE *infile, FILE *outfile){

    char line[100];
    int c;

    fgets(line,100,infile);
    c=strlen(line);

    while(line[c]!='\n' && line[c-1]!='5' && line[c-2]!='5' && line[c-3]!='2'){
            if(line[0]=='#'){
                    fgets(line,100,infile);
                    c=strlen(line);
            }
            else{
                    fputs(line,outfile);
                    fgets(line,100,infile);
                    c=strlen(line);
                 }
        }
        fputs(line,outfile);
}

The issue I am running into is that I have two .ppm files with similar header formats, but the one with 561 by 375 dimensions does not output the last line with 255 onto the new file. Is there a difference between these two files that is affected by my code?

Here is the .ppm file that does not copy over the 255 line

Here is the .ppm file that does copy the 255 line

.ppm file that works

.ppm file that does not work

Answer 1

The while conditions are wrong. Since c is the length of the string, line[c] points to the null character that ends it. It can never be '\\n' . And line[c-1] is the '\\n' that ends a line (except possibly for the last line in a file), so it is never '5' (unless the last line ends with '5' ). And of course line[c-2] and line[c-3] are also out of position.

What you actually want is:

while (! (4 <= c && line[c-4] == '2' && line[c-3] == '5' && line[c-2] == '5' && line[c-1] == '\n')) {

With some improvements:

void headerinfo(FILE *infile, FILE *outfile)
{
    char line[100];
    size_t c;

    do
    {
        fgets(line, sizeof line, infile);
        c = strlen(line);
        if (line[0] != '#')
            fputs(line, outfile);
    } while (! (4 <= c && strcmp(&line[c-4], "255\n") == 0));
}