temp=tmpfile() lose all its contents?

[learner007]

Dear there,

I wrote a simple all->unix ascii file converter on fly, see the comments below. I am using temp=tmpfile() to hold contents for later processing, but it seems lost later on.

/* FILE* file is assigned before calling this routing. 
After calling this routine, 'file; is supposed to point to the temporary file stream 
with processed content. However, I found later that file has no content at all.
*/
 
/** 
 * simple text convert: convert all to Unix line ending
 * I use fgets() to read a line, which stops whenever \n (LF) is met. However, different line ending could be used:
 * DOS/Windows: CR LF
 * Unix: LF
 * MAC OS X: LF
 * MAC (prior to MAC OS X): CR
 * this convert is simple since it is only for use with fgets(), strtok(), and strtof()
 * strtok() will skip leading 'sep' when processing tokens, in this file sep=' \t,'; strtof() will
 * skip leading white space as specified by isspace(). Hence I replace CR LF with LF SPACE; and CR with LF.
 */
void trimcarriage(){
  FILE* temp=tmpfile();//see p483 k.n.king
  int ch, chnext;
  while(ch=getc(file) != EOF){
    if (ch != '\r'){//straight copy
      putc(ch, temp);
    }else{
      putc('\n',temp);//replace it with \n
      if (chnext=getc(file) != '\n'){
    ungetc(chnext, file);//put it (including EOF) back
      }//otherwise '\n' is not wrote into temp
    }
  }
  fclose(file);
  rewind(temp);
  file=temp;
}
 

[weaknessforcats]

Are temp and file both FILE* to the same file?

If so, you have a problem because you cannot have two active FILE* to the same file.

[learner007]

I found the mistake in the statement:
ch=getc(file) != EOF
which should be
(ch=getc(file)) != EOF
due to operator precedence.