CODEWITHSUNDEEP
cfile-ioprintffdopen
Elfayer
Elfayer

Reputation: 4571

How to fdopen as open with the same mode and flags?

I would like to have a FILE* type to use fprintf. I need to use fdopen to get a FILE* instead of open that returns an int. But can we do the same with fdopen and open? (I never used fdopen)

I would like to do a fdopen that does the same as :

open("my_file", 0_CREAT | O_RDWR | O_TRUNC, 0644);

Upvotes: 6

Views: 24884

Answers (3)

Grijesh Chauhan
Grijesh Chauhan

Reputation: 58291

fdopen()use file descriptor to file pointer:

The fdopen() function associates a stream with a file descriptor. File descriptors are obtained from open(), dup(), creat(), or pipe(), which open files but do not return pointers to a FILE structure stream. Streams are necessary input for almost all of the stdio library routines.

FILE* fp = fdopen(fd, "w");

this example code may help you more as you want to use fprintf():

int main(){
 int fd;
 FILE *fp;
 fd = open("my_file",O_WRONLY | O_CREAT | O_TRUNC);
  if(fd<0){
    printf("open call fail");
    return -1;
 }
 fp=fdopen(fd,"w");
 fprintf(fp,"we got file pointer fp bu using File descriptor fd");
 fclose(fp);
 return 0;
}

Notice:

Upvotes: 9

bash.d
bash.d

Reputation: 13217

If you don't have previously acquired a file-descriptor for your file, rather use fopen.

FILE* file = fopen("pathtoyourfile", "w+");

Consider, that fopen is using the stand-library-calls and not the system-calls (open). So you don't have that many options (like specifying the access-control-values).

See the man-page.

Upvotes: 1

Blagovest Buyukliev
Blagovest Buyukliev

Reputation: 43558

fdopen takes a file descriptor that could be previously returned by open, so that is not a problem.

Just open your file getting the descriptor, and then fdopen that descriptor.

fdopen simply creates a userspace-buffered stream, taking any kind of descriptor that supports the read and write operations.

Upvotes: 9

Related Questions