假设我将UTF-8内容存储在内存中,如何使用指针读取字符？我认为我需要注意第8位表示多字节字符,但我究竟如何将序列转换为有效的Unicode字符？另外,wchar_t是否存储单个Unicode字符的正确类型？
这就是我的想法：
wchar_t readNextChar (char*& p)
{
wchar_t unicodeChar;
char ch = *p++;
if ((ch & 128) != 0)
{
// This is a multi-byte character,what do I do now?
// char chNext = *p++;
// ... but how do I assemble the Unicode character?
...
}
...
return unicodeChar;
}
解决方法
您必须将UTF-8位模式解码为其未编码的UTF-32表示.如果需要实际的Unicode代码点,则必须使用32位数据类型.
在Windows上,wchar_t不够大,因为它只有16位.您必须使用unsigned int或unsigned long.仅在处理UTF-16代码单元时才使用wchar_t.
在其他平台上,wchar_t通常为32位.但是在编写可移植代码时,你应该远离wchar_t,除非绝对需要(比如std :: wstring).
尝试更像这样的东西：
#define IS_IN_RANGE(c,f,l) (((c) >= (f)) && ((c) <= (l)))
u_long readNextChar (char* &p)
{
// TODO: since UTF-8 is a variable-length
// encoding,you should pass in the input
// buffer's actual byte length so that you
// can determine if a malformed UTF-8
// sequence would exceed the end of the buffer...
u_char c1,c2,*ptr = (u_char*) p;
u_long uc = 0;
int seqlen;
// int datalen = ... available length of p ...;
/*
if( datalen < 1 )
{
// malformed data,do something !!!
return (u_long) -1;
}
*/
c1 = ptr[0];
if( (c1 & 0x80) == 0 )
{
uc = (u_long) (c1 & 0x7F);
seqlen = 1;
}
else if( (c1 & 0xE0) == 0xC0 )
{
uc = (u_long) (c1 & 0x1F);
seqlen = 2;
}
else if( (c1 & 0xF0) == 0xE0 )
{
uc = (u_long) (c1 & 0x0F);
seqlen = 3;
}
else if( (c1 & 0xF8) == 0xF0 )
{
uc = (u_long) (c1 & 0x07);
seqlen = 4;
}
else
{
// malformed data,do something !!!
return (u_long) -1;
}
/*
if( seqlen > datalen )
{
// malformed data,do something !!!
return (u_long) -1;
}
*/
for(int i = 1; i < seqlen; ++i)
{
c1 = ptr[i];
if( (c1 & 0xC0) != 0x80 )
{
// malformed data,do something !!!
return (u_long) -1;
}
}
switch( seqlen )
{
case 2:
{
c1 = ptr[0];
if( !IS_IN_RANGE(c1,0xC2,0xDF) )
{
// malformed data,do something !!!
return (u_long) -1;
}
break;
}
case 3:
{
c1 = ptr[0];
c2 = ptr[1];
switch (c1)
{
case 0xE0:
if (!IS_IN_RANGE(c2,0xA0,0xBF))
{
// malformed data,do something !!!
return (u_long) -1;
}
break;
case 0xED:
if (!IS_IN_RANGE(c2,0x80,0x9F))
{
// malformed data,do something !!!
return (u_long) -1;
}
break;
default:
if (!IS_IN_RANGE(c1,0xE1,0xEC) && !IS_IN_RANGE(c1,0xEE,0xEF))
{
// malformed data,do something !!!
return (u_long) -1;
}
break;
}
break;
}
case 4:
{
c1 = ptr[0];
c2 = ptr[1];
switch (c1)
{
case 0xF0:
if (!IS_IN_RANGE(c2,0x90,do something !!!
return (u_long) -1;
}
break;
case 0xF4:
if (!IS_IN_RANGE(c2,0x8F))
{
// malformed data,0xF1,0xF3))
{
// malformed data,do something !!!
return (u_long) -1;
}
break;
}
break;
}
}
for(int i = 1; i < seqlen; ++i)
{
uc = ((uc << 6) | (u_long)(ptr[i] & 0x3F));
}
p += seqlen;
return uc;
}
