unicode转utf8

场景:

1.有些字符串编码是unicode的，但是第3方库需要的是utf8字符串，这时候就需要unicode转utf8的接口了。

//unicodeתutf8
#include <iostream>
#include <fstream>


using namespace std;

#define MAX_LENGTH 1024


int UniCharToUTF8(wchar_t UniChar, char* OutUTFString)
{
	int UTF8CharLength = 0;

	if (UniChar < 0x80)
	{ 
		if ( OutUTFString )
			OutUTFString[UTF8CharLength++] = (char)UniChar;
		else
			UTF8CharLength++;
	}
	else if(UniChar < 0x800)
	{
		if ( OutUTFString )
		{
			OutUTFString[UTF8CharLength++] = 0xc0 | ( UniChar >> 6 );
			OutUTFString[UTF8CharLength++] = 0x80 | ( UniChar & 0x3f );
		}
		else
		{
			UTF8CharLength += 2;
		}
	}
	else if(UniChar < 0x10000 )
	{
		if ( OutUTFString )
		{
			OutUTFString[UTF8CharLength++] = 0xe0 | ( UniChar >> 12 );
			OutUTFString[UTF8CharLength++] = 0x80 | ( (UniChar >> 6) & 0x3f );
			OutUTFString[UTF8CharLength++] = 0x80 | ( UniChar & 0x3f );
		}
		else
		{
			UTF8CharLength += 3;
		}
	}
	else if( UniChar < 0x200000 )
	{
		if ( OutUTFString )
		{
			OutUTFString[UTF8CharLength++] = 0xf0 | ( (int)UniChar >> 18 );
			OutUTFString[UTF8CharLength++] = 0x80 | ( (UniChar >> 12) & 0x3f );
			OutUTFString[UTF8CharLength++] = 0x80 | ( (UniChar >> 6) & 0x3f );
			OutUTFString[UTF8CharLength++] = 0x80 | ( UniChar & 0x3f );
		}
		else
		{
			UTF8CharLength += 4;
		}
	}

	return UTF8CharLength;
}


void main()
{
	FILE* pFile=fopen("E:/project/11111/Debug/11.txt","r");
	fseek(pFile, 2, SEEK_SET);

	long int file_length = 0;
	int index = 1;
	char* pBuf;
	pBuf = (char*)calloc(1, MAX_LENGTH);
	char* curr_buf;

	wchar_t w_ch=fgetwc(pFile);
	while(!feof(pFile))
	{   
		if(file_length + 6 > index * MAX_LENGTH)
		{
			index++;
			realloc(pBuf, index * MAX_LENGTH);
		}
		curr_buf = pBuf + file_length;
		file_length += UniCharToUTF8(w_ch, curr_buf);
		
		printf("%s", curr_buf);
		w_ch=fgetwc(pFile);   
	}
	pBuf[file_length] = '\0';
	fclose(pFile);

	getchar();
}