I want to open a file for writing, but if the file already exists, fail rather than overwriting it.
I know I could do something like this.....
if ((fileP = fopen(filename, "r")) != NULL)
{
fclose (fileP);
printf ("file already exists");
}
else
{
if ((fileP = fopen(filename, "w")) != NULL)
{
printf ("created file");
}
else
{
printf ("couldn't create file");
}
}
(and I could use stat() rather than fopen)....problem is, neither of these are atomic, in that the file could technically be created in between the calls to fclose and fopen by another process. What's the best way to do this?
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use the lower-level open() call instead, passing the O_WRONLY | O_CREAT | O_EXCL flags:
O_CREAT create file if it does not exist
O_EXCL error if create and file exists
The following opens the file with exclusive create, then associates the returned file descriptor
with a buffered stream:
FILE *fileP = NULL;
int fd = -1;
if ((fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, mode)) != -1) {
fileP = fdopen(fd, "w")
}
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by: darkrainPosted on 2004-01-25 at 16:51:03ID: 10198042
Try this way
FILE *TEST;
TEST = fopen(filename ,"r");
if (TEST == NULL)
{
TEST = fopen(filename ,"w");
iCloseSucess = fclose(infClubber);
if (iCloseSucess ==0)
{
printf("\File Created");
}
else
{
printf("file already exists");
}
}
a bit simple but it might help