前几天接了个任务做POP3的邮件编码转换，本来感觉是很简单的事情，但是总共还是花了三天时间才做到自己比较满意的效果。

简单记录下遇到的几个坑，也许对别人有帮助。

1、入参改变的问题

iconv的函数定义如下：

#include

size_t iconv(iconv_t cd,

char **inbuf, size_t *inbytesleft,

char **outbuf, size_t *outbytesleft);

看下man里面的说明，可以通过man 3 iconv获取，简单翻译下重点，就是在转换的时候会逐个字节读取inbuf的值，并会对其值做改变，同时减少Inbyteleft字节数，将结果写入到outbuf中，增加outbuf，outbytesleft逐渐减小，入参的改变要特别小心，如果你的outbuf要释放，就不能直接传递进去，因为一旦发生了改变，free()的时候就会core掉，所以一般都是传递临时指针给它们。

The iconv() function converts one multibyte character at a time, and for each character conversion it increments *inbuf and decrements *inbytesleft by the num‐

ber 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. If the character encoding of the input is stateful, the iconv() function can also convert a sequence of input bytes to an update to the con‐

version state without producing any output bytes; such input is called a shift sequence. The conversion can stop for four reasons:

1. An invalid multibyte sequence is encountered in the input. In this case it sets errno to EILSEQ and returns (size_t) -1. *inbuf is left pointing to the

beginning of the invalid multibyte sequence.

2. The input byte sequence has been entirely converted, that is, *inbytesleft has gone down to 0. In this case iconv() returns the number of nonreversible

conversions performed during this call.

3. An incomplete multibyte sequence is encountered in the input, and the input byte sequence terminates after it. In this case it sets errno to EINVAL and

returns (size_t) -1. *inbuf is left pointing to the beginning of the incomplete multibyte sequence.

4. The output buffer has no more room for the next converted character. In this case it sets errno to E2BIG and returns (size_t) -1.

2、类型的问题

传入参数的数据类型一定要是对的，不能做强制转换，不然可能会发生core的问题，我就遇到过一次。

3、例子

#include

#include

#include

#include

static int charset_convert(char *inbuf,size_t inlen,char *outbuf,size_t * poutlen,char * from_charset,char * to_charset)

{

iconv_t cd;

char **pin = &inbuf;

char **pout = &outbuf;

int outlen = * poutlen;

cd = iconv_open(to_charset,from_charset);

if (cd == (iconv_t)-1) {

perror("open error");

return -1;

}

memset(outbuf,0,outlen);

if (iconv(cd,pin,&inlen,pout,poutlen) == -1) {

perror("Iconv error");

}

iconv_close(cd);

return 0;

}

int main(void)

{

int r;

char *sin, *sout;

size_t lenin, lenout;

char src []= {0xc3,0xf7,0xd2,0xed,0x00};

char dst[16] = {0};

iconv_t c_pt;

sin = src;

lenin = strlen(src);

sout = dst;

lenout = 16;

printf("len:%d\n",lenin);

charset_convert(src,lenin,dst,&lenout,"GB18030","UTF-8");

printf("start:%d len:%d SRC[%s], DST[%s].\n",lenin,lenout, src, dst);

return 0;

}