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Tor Rustad  
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 More options Jun 11 2009, 7:37 pm
Newsgroups: comp.lang.c
From: Tor Rustad <bwz...@wvtqvm.vw>
Date: Fri, 12 Jun 2009 01:37:10 +0200
Local: Thurs, Jun 11 2009 7:37 pm
Subject: Re: rtf file verification
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Cross wrote:
> Hello

> I am writing a program to verify if it is an rtf file or not. Now, an rtf file
> starts with {\rtf<N>.

> My code is as follows:
> int main(int argc, char **argv){
>    char str[5], c;
>    FILE *fstream

>    //code for connecting to file stream

>    c=getc(fstream);

return type of getc() is int, not char. Need to check for EOF.

>    if(c!='{'){
>     // An rtf file should start with `{\rtf'
>    fprintf(stderr, "invalid rtf file\n");
>    }else if(fscanf(fstream, "%4s", &str), strcmp(str, "\rtf")!=0 ){

'&str' is wrong, could use '&str[0]' or 'str'.

using comma operator here is terrible for readability and wrong, in case
of read error you invoke UB.

>    fprintf(stderr, "rtf version unspecified.\n");
>     // check: if str prints "\rtf", why strcmp returns non-zero value?

others have answered that...

>    printf("%s\n", str);
>    }else{
>    // stuff to do
>    }
>    return 0;
> }

> I tried to check the code against an rtf file. The "\rtf" tag check fails

/**
  * check if file has prefix "{\rtf"
  */
int is_rtf(FILE *f)
{
         char            buf[6]={0};
         const char      *prefix = "{\\rtf";

         if (NULL == fgets(buf, sizeof buf, f)) {
                 perror("is_rtf()");
                 exit(EXIT_FAILURE);
         }

         return 0==strcmp(prefix, buf);

}

--
Tor <echo bwz...@wvtqvm.vw | tr i-za-h a-z>

 
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