Iterating over multiple file objects

Question

I would like to iterate over a list/array of file objects: file_x,file_y,file_z,..., calling a function on each file object, in C.

Question

How can I create a function that would take (i) file object, and (ii) a string as arguments to the function and then write the string to that file object. A For loop could then execute the function over a list/array of file objects.

void file_write(file_object, string_to_write){
   fprintf(file_object, "%s\n", string_to_write);
}

Research

I have searched Google, watched parts of several Youtube tutorials and searched for relevant questions on SO, but the following is the best I could achieve. Any advice on how to better answer the above question, with the ideal function, would be much appreciated.

FILE *file_x, *file_y, *file_z, *file_vx, *file_vy

file_x  = fopen("./data/x.dat","w"); 
file_y  = fopen("./data/y.dat","w"); 
file_z  = fopen("./data/z.dat","w"); 
file_vx = fopen("./data/vx.dat","w"); 
file_vy = fopen("./vy.dat","w"); 

fprintf(file_x,  "#X(t) Coordinates\n#Time (t)\n");
fprintf(file_y,  "#Y(t) Coordinates\n#Time (t)\n");
fprintf(file_z,  "#Z(t) Coordinates\n#Time (t)\n");
fprintf(file_vx, "#X(t) Velocities\n#Time (t)\n");
fprintf(file_vy, "#Y(t) Velocities\n#Time (t)\n");

fclose(file_x);
fclose(file_y);
fclose(file_z);
fclose(file_vx);
fclose(file_vy);

Here: void file_write(file_object, string_to_write){, is file_object supposed to be an array of FILE* or a single FILE*? — Spikatrix
– Spikatrix, Commented Oct 10, 2015 at 9:03
@CoolGuy preferably the single one, but then I would greatly appreciate if you could also explain how to create an array of file objects, outside of the function. Is it possible to create an array of files? — hello_there_andy
– hello_there_andy, Commented Oct 10, 2015 at 9:06
You could try to use a two dimension array or a one dimension arry to a char* to store all the file name/path and use indexes to refer to them as char *fileName[num of files] = {"path/name", ...}; This way you can use a for loop to open them and store the opened file descriptor to another array which you can another for loop to loop through can call your function. — SSC
– SSC, Commented Oct 10, 2015 at 9:17
void file_write(FILE *file_object, const char *string_to_write) — melpomene
– melpomene, Commented Oct 10, 2015 at 9:32

machine_1 · Accepted Answer · 2015-10-10 10:40:46Z

4

you declare a single FILE pointer and then,you can declare two arrays,one for file names,and one for the data to be written to them.make a loop and iterate like this :

int main(void)
{
    FILE *file_x;

    const char *dirs[] = { "./data/x.dat",
                           "./data/y.dat",
                           "./data/z.dat",
                           "./data/vx.dat",
                           "./vy.dat"
                         };

    const char *data[] = { "#X(t) Coordinates\n#Time (t)\n",
                           "#Y(t) Coordinates\n#Time (t)\n",
                           "#Z(t) Coordinates\n#Time (t)\n",
                           "#X(t) Velocities\n#Time (t)\n",
                           "#Y(t) Velocities\n#Time (t)\n",
                         };

    for( int n = 0 ; n < 5 ; n++ )
    {
        file_x = fopen(dirs[n],"w");

        if ( !file_x )
        {
            perror(dirs[n]);
            exit(EXIT_FAILURE);
        }
        fprintf(file_x , "%s" , data[n]);

        fclose(file_x);
    }
    return 0;
}

edited Oct 10, 2015 at 10:40

answered Oct 10, 2015 at 9:32

machine_1

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11 Comments

Jongware Over a year ago

You open only one file at a time, process it and then close immediately, so you only need a single FILE *.

hello_there_andy Over a year ago

@machine_1 thanks for the answer, but the code as it is shown in the answer is leading to a seg fault works on it

melpomene Over a year ago

That should be fprintf(file_x, "%s", data[n]);. Never use fprintf without a literal format string.

melpomene Over a year ago

You should also check whether fopen succeeded: if (!file_x) { perror(dirs[n]); exit(EXIT_FAILURE); }

melpomene Over a year ago

@hello_there_andy Change char * to const char *.

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