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kavi · #1 (**permalink**) 15-10-2005, 11:25 AM

Hi friends,
I have a small question. I have a data file. Depending on the application i need to pass an argument to my program(C program), which is n (2,4,8,16,etc). Now based on this input argument n, i need to perform some operations on the data file and write the output to n different files. How do i create new files dynamically ( based on user input n)?

rockdalinux · #2 (**permalink**) 15-10-2005, 02:14 PM

You mean you need uniq file name each time and then write output to that file?

charvi · #3 (**permalink**) 15-10-2005, 02:35 PM

If you wanna make a unique file you can use mkstemp()

Code:

int main()
{
        char sfn[] = "myapplication.XXXXXX";
        int fd;
        fd=mkstemp(sfn);
}

Just run ls -l command in current dir to see unique file and use fd to open file in code. But i'm not clear what kavi is looking for, may we need bit more info...

kavi · #4 (**permalink**) 16-10-2005, 06:05 AM

Quote:

Originally Posted by rockdalinux

You mean you need uniq file name each time and then write output to that file?

yes i will need unique file names. for example, the input arg is 8 then i have to perform different operations and write outputs to 8 different new output files.

kavi · #5 (**permalink**) 16-10-2005, 06:12 AM

Quote:

Originally Posted by charvi

If you wanna make a unique file you can use mkstemp()

Code:

int main()
{
        char sfn[] = "myapplication.XXXXXX";
        int fd;
        fd=mkstemp(sfn);
}

Just run ls -l command in current dir to see unique file and use fd to open file in code. But i'm not clear what kavi is looking for, may we need bit more info...

Hi charvi,
Thank for the clues. I will try to elaborate with an example. Lets say i write a program divide.c which takes input argument n(2,4,8,16,etc). First thing i do is open an input data file. Then depending on n, i will perform some math on every M bytes of data file and get n different outputs. Now i would like to write each of these n outputs in n different files.
Note: i am performing n operations on every M bytes and there will be n output for every M bytes of the data file. I will be appending data to n files every time

tom · #6 (**permalink**) 16-10-2005, 04:22 PM

hope foillowing will code help you

Code:

#include <errno.h>
int main(int a, char *v[])
{
        char sfn[] = "/tmp/myapplication.XXXXXX";
        FILE *f;
        int fd=-1;
        int i=0,m=0;
        // if not sufficent args
        if (a < 2 )
        {
                fprintf(stderr, "%s %s %s\n", "Error: Argument missing\nSyntax:\n",
                                v[0],"{number}");
                exit(1);
        }

        // put loop to create files
        m=atoi(v[1]);
        for(;i<m;i++){
                sprintf(sfn,"%s%d.XXXXXX","/tmp/file",i);
                fd = mkstemp(sfn);
                if (( f = fdopen(fd, "w+")) == NULL ){
                        fprintf(stderr, "%s\n", "Failed to open file");
                        perror("Error : ");
                        close(fd);
                        exit(2);
                }
                printf("Using file %s\n",sfn);
                fprintf(f,"This is test data %d\n",i);
                fflush(f);
                close(fd);
                // before removing file you need to copy the tmp file to data dir
                // else you will lost the data stored in /tmp/file* file
                unlink(sfn);
        }
}

it need to run as

Code:

cc test.c
./a.out 5

and it will create five files in /tmp directory, make sure before unlink you copy back data file using API as we cannnot open too many files aka FDs.

charvi · #7 (**permalink**) 16-10-2005, 04:34 PM

wow tom, u extended my 4 line code to big one

now why the hell you used ulink() at the end

as far as i know it will remove file ... may be you need to through some light coz i'm not able to get your idea, rest of program is fine

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