Question

I try to make method which converts s-jis string to utf-8 string using iconv.
I wrote a code below,

#include <iconv.h>
#include <iostream>
#include <stdio.h>
using namespace std;

#define BUF_SIZE 1024
size_t z = (size_t) BUF_SIZE-1;

bool sjis2utf8( char* text_sjis, char* text_utf8 )
{
  iconv_t ic;
  ic = iconv_open("UTF8", "SJIS"); // sjis->utf8
  iconv(ic , &text_sjis, &z, &text_utf8, &z);
  iconv_close(ic);
  return true;
}
int main(void)
{
  char hello[BUF_SIZE] = "hello";
  char bye[BUF_SIZE] = "bye";
  char tmp[BUF_SIZE] = "something else";

  sjis2utf8(hello, tmp);
  cout << tmp << endl;

  sjis2utf8(bye, tmp);
  cout << tmp << endl;
}

and, output should be

hello
bye

but in fact,

hello
hello

Does anyone know why this phenomenon occurs? What’s wrong with my program?

Note that “hello” and “bye” are Japanese s-jis strings in my original program, but I altered it to make program easy to see.

Answer 1

I think you are misusing the iconv function by passing it the global variable z. The first time you call sjis2utf8, z is decremented to 0. The second call to sjis2utf8 have no effect (z==0) and leaves tmp unchanged.

From the iconv documentation :

size_t iconv (iconv_t cd,
              const char* * inbuf, size_t * inbytesleft,
              char* * outbuf, size_t * outbytesleft);

The iconv function converts one multibyte character at a time, and for each character conversion it increments *inbuf and decrements *inbytesleft by the number of converted input bytes, it increments *outbuf and decrements *outbytesleft by the number of converted output bytes, and it updates the conversion state contained in cd.

You should use two separate variables for the buffers lengths :

size_t il = BUF_SIZE - 1 ;
size_t ol = BUF_SIZE - 1 ;

iconv(ic, &text_sjis, &il, &text_utf8, &ol) ;

Then check the return value of iconv and the buffers lengths for the conversion success.