CODEWITHSUNDEEP
cfile-io
Aditya Somani
Aditya Somani

Reputation: 191

How to check if file already has data (in C)?

I am trying to write a simulation program in C where I am appending a file by opening it in append mode. This file is a csv (comma separated values).

I would like to write the headings of my simulation information before I write the actual values so that they don't seem unrelated. Is there an easy way to do this?

For example:

Central Node, System Delay, Bandwidth Requirement

14,240,11

4,285,23

13,300,9

My code looks like this:

void Data_Output(FILE *fp){
struct stat buf;
FILE fd = *fp;
fstat(fd, &buf);
fprintf(stderr,"DEBUG------%d\n",buf.st_size);
}

The output error I get is:

ff.c: In function ‘Data_Output’:
ff.c:296:2: error: incompatible type for argument 1 of ‘fstat’
fstat(fd, &buf);
^
In file included from /usr/include/stdio.h:29:0,
             from ff.c:1:
/usr/include/sys/stat.h:148:5: note: expected ‘int’ but argument is of type ‘FILE’
 int _EXFUN(fstat,( int __fd, struct stat *__sbuf ));
 ^
Makefile:7: recipe for target 'ff.o' failed
make: *** [ff.o] Error 1

What am I doing wrong? Should I be typecasting it in order to make it work?

Upvotes: 2

Views: 293

Answers (3)

mrjoltcola
mrjoltcola

Reputation: 20842

fstat() works on an integer low level file descriptor, not a FILE * / stream. You need to obtain the descriptor from the FILE * (fp) and use that.

Try:

int fd = fileno(fp);
fstat(fd, &buf);

Upvotes: 1

Guru
Guru

Reputation: 1410

You can check size of a file. For more info how to get size you can check check this post

Upvotes: 1

Arjun Sreedharan
Arjun Sreedharan

Reputation: 11453

You can use the fstat() function to dump the stats to a buffer, which would contain the size of the file under st_size.

Upvotes: 0

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