Redirecting stdin to a temporary file?

Question

I want stdin to be redirected to a string of text supplied in my program. I want to write the string of text to a temporary file and then point stdin to that file. I'm a little unsure about this code because it seems to blend low level function calls like write() and dup() with higher level function calls like fclose(). Is this the correct approach?:

char* buffer = "This is some text";
int nBytes = strlen(buffer);
FILE* file = tmpfile();
int fd = fileno(file);
write(fd,buffer,nBytes);
rewind(file);
dup2(fd,0);
fclose(file);

EDIT

As per a suggestion in the comments, I tried approaching this problem with pipes. If I want to use pipes, would this be the correct approach? I still want feedback on the first approach as well:

int fd[2];
pipe(fd); // For sake of simplicity assume returns 0 (no error).
char* buffer = "This is some text";
int nBytes = strlen(buffer);
write(fd[1],buffer,nBytes);
close(fd[1]);
dup2(fd[0],0);
close(fd[0]);

To find it out, you will need to compile that code and execute it. — mcleod_ideafix, Nov 21 '13 at 17:35
You already have your string in RAM, why would you copy it to a file and then read it back to RAM? — n. m. could be an AI, Nov 21 '13 at 17:41
Because later I am going to run `execvp()` and I want this string to be read in by the command I invoke. — Kvass, Nov 21 '13 at 17:42
If you cannot do a pipe for some reason, use `mkstemp` and sidestep stdio entirely. — n. m. could be an AI, Nov 21 '13 at 18:01
Can you show how this example would work with `mkstemp`? Alternatively, can you demonstrate how this example would work with pipes? I'm not very familiar with them. — Kvass, Nov 21 '13 at 18:13
`mkstemp` just gives you an open file descriptor, sidestepping `FILE*` (use `man mkstemp` to read more). I cannot give a tutorial on pipes in this small box. — n. m. could be an AI, Nov 21 '13 at 18:37
Are you sure you are not looking for [`freopen`](http://www.manpagez.com/man/3/freopen/) ? Also check this answer http://stackoverflow.com/questions/584868/rerouting-stdin-and-stdout-from-c — Shiplu Mokaddim, Nov 21 '13 at 19:00
Would follow this http://stackoverflow.com/questions/14543443/in-c-how-do-you-redirect-stdin-stdout-stderr-to-files-when-making-an-execvp-or — Kevin Wang, Nov 21 '13 at 19:10

Redirecting stdin to a temporary file?

0 Answers0