Re: string types

[Tim Rühsen]

On 27.12.19 11:51, Bruno Haible wrote:
> Aga wrote:
>> I do not know if
>> you can (or if it is possible, how it can be done), extract with a way a 
>> specific
>> a functionality from gnulib, with the absolute necessary code and only that.
> 
> gnulib-tool does this. With its --avoid option, the developer can even 
> customize
> their notion of "absolutely necessary".
> 
>> In a myriad of codebases a string type is implemented at least as:
>>   size_t mem_size;
>>   size_t num_bytes;
>>   char *bytes;
> 
> This is actually a string-buffer type. A string type does not need two size_t
> members. Long-term experience has shown that using different types for string
> and string-buffer is a win, because
>   - a string can be put in a read-only virtual memory area, thus enforcing
>     immutability (-> reducing multithread problems),
>   - providing primitives for string allocation reduces the amount of buffer
>     overflow bugs that otherwise occur in this area. [1]
> [1] https://lists.gnu.org/archive/html/bug-gnulib/2019-09/msg00031.html
>

Just FYI,

here is a string concatenation function without ellipsis, analogue to
writev() and struct iovec - just a suggestion. Instead of 'struct
strvec' a new string_t type would be handy.

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct strvec {
  char *strv_base;
  size_t strv_len;
};

__attribute__ ((nonnull (1)))
char *concat_stringv(const struct strvec *strv)
{
  const struct strvec *str;
  size_t len = 0;
  char *buf;

  for (str = strv; str->strv_base; str++)
    len += str->strv_len;

  if (!(buf = malloc(len + 1)))
    return buf;

  len = 0;
  for (str = strv; str->strv_base; len += str->strv_len, str++)
    memcpy(buf + len, str->strv_base, str->strv_len);

  buf[len] = 0;

  return buf;
}

void main(void)
{
  char *s = concat_stringv((struct strvec []) {
    { "a", 1 },
    { "b", 1 },
    { NULL }
  });

  puts(s);

  free(s);
}


In GNU Wget2 we already have type similar to string_t. Just used in
cases where we need pointer + len of URLs inside const HTML/XML/CSS data.

typedef struct {
        const char
                *p; //!< pointer to memory region
        size_t
                len; //!< length of memory region
} wget_string;


So maybe we need a string_t and a const_string_t type !? (to avoid
casting from const char *)

Regards, Tim

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