Re: [Groff] Readable tbl-source

[Werner LEMBERG]

>          1  char *string::extract() const
>          2  {
>          3    char *p = ptr;
>          4    int n = len;
>          5    int nnuls = 0;
>          6    int i;
>          7    for (i = 0; i < n; i++)
>          8      if (p[i] == '\0')
>          9        nnuls++;
>         10    char *q = new char[n + 1 - nnuls];
>         11    char *r = q;
>         12    for (i = 0; i < n; i++)
>         13      if (p[i] != '\0')
>         14        *r++ = p[i];
>         15    q[n] = '\0';
>         16    return q;
>         17  }
> 
> Does `new char[n]' give memory pre-filled with '\0'?  I guess not
> because #15 puts the terminating '\0' in place.  But if on entry ptr ==
> "a\0c\0" and len == 3

No.  len == 4 for "a\0b\0".  In a `string' class, strings aren't
null-terminated; if there is a trailing \0, it is part of the string.

> [...]
>
> Assuming I'm right that then...
> 
>         19  void string::remove_spaces()
>         20  {
>         21    int l = len - 1;
>         22    while (l >= 0 && ptr[l] == ' ')
>         23      l--;
>         24    char *p = ptr;
>         25    if (l > 0)
>         26      while (*p == ' ') {
>         27        p++;
>         28        l--;
>         29      }
>         30    if (len - 1 != l) {
>         31      if (l >= 0) {
>         32        len = l + 1;
>         33        char *tmp = new char[len];
>         34        memcpy(tmp, p, len);
>         35        a_delete ptr;
>         36        ptr = tmp;
>         37      }
>         38      else {
>         39        len = 0;
>         40        if (ptr) {
>         41          a_delete ptr;
>         42          ptr = 0;
>         43        }
>         44      }
>         45    }
>         46  }
> 
> given ptr == "abc \0" and len == 4 by #33 len == 3 and #34 will copy
> "abc" without a '\0' character on the end.

During the parsing of tbl items, no \0 is appended; remove_spaces will
see "abc " (with len == 4), converting it to "abc".

> The two routines don't seem to match in terms of what ptr holds, a
> \0 terminated string or not.

A trailing \0 must be explicitly inserted if necessary.


    Werner