From: richard.nospam@gmail.invalid

On 06/12/2025 01:05, Michael Sanders wrote:
> Am I close? Missing anything you'd consider to be (or not) needed?

A text file is supposed to end with a '\n' (M$, of course, largely
ignores this convention), but a quick test could be:

         f = fopen(path, "rb");

         fseek(f, -1, SEEK_END);

         if ( (c = fgetc(f)) == '\n' )
             printf("Text\n");
         else
             printf("Binary\n");

         fclose(f);

Be aware of false positives/negatives, because I'm sure there will be
plenty :)


>
> 
>
> /*
>   * Checks if a file is likely a binary by examining its content
>   * for NULL bytes (0x00) or unusual control characters.
>   * Returns 0 if text, 1 if binary or file open failure.
>   */
>
> int is_binary_file(const char *path) {
>      FILE *f = fopen(path, "rb");
>      if (!f) return 1; // cannot open file, treat as error/fail check
>
>      unsigned char buf[65536];
>      size_t n, i;
>
>      while ((n = fread(buf, 1, sizeof(buf), f)) > 0) {
>          for (i = 0; i < n; i++) {
>              unsigned char c = buf[i];
>
>              // 1. check for the NULL byte (strong indicator of binary data)
>              if (c == 0x00) {
>                  fclose(f);
>                  return 1; // IS binary
>              }
>
>              // 2. check for C0 control codes (0x01-0x1F), excluding known
>              // text formatting characters: 0x09 (Tab), 0x0A (LF), 0x0D (CR)
>              if (c < 0x20) {
>                  if (c != 0x09 && c != 0x0A && c != 0x0D) {
>                      fclose(f);
>                      return 1; // IS binary (contains unexpected control
code)
>                  }
>              }
>          }
>      }
>
>      fclose(f);
>      return 0; // NOT binary
> }
>

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