23. fread和fwrite的读写缓冲区

fwrite(buff, sizeof(buff), 1, pFile);//返回实际写入的完整项数，参数3尽量填1，简单粗暴
fread(buff, sizeof(buff), 1, pFile);//返回实际读取的完整项数，参数3尽量填1，简单粗暴

FILE *pFileSource = fopen("C++ Primer.exe", "rb");//CreateFile
FILE *pFileDest = fopen("C++ Primer2.exe", "wb");

char buffSource[16] = { 0 };//设置很小的缓冲区，便于测试
char buffDest[16] = { 0 };
setvbuf(pFileSource, buffSource, _IOFBF, 7);//只给7字节，便于测试
setvbuf(pFileDest, buffDest, _IOFBF, 7);

fseek(pFileSource, 0, SEEK_END);
long fileSize = ftell(pFileSource);

rewind(pFileSource);
unsigned int buff = 0;
for (long i = 0; i < fileSize / 4; i++) {
    fread(&buff, sizeof(buff), 1, pFileSource);//ReadFile
    fwrite(&buff, sizeof(buff), 1, pFileDest);//直接写入缓冲区，满了调用flush
}
unsigned char byte = '';
for (long i = 0; i < fileSize % 4; i++) {
    fread(&byte, sizeof(byte), 1, pFileSource);
    fwrite(&byte, sizeof(byte), 1, pFileDest);
}

fflush(pFileDest);//WriteFile
fclose(pFileSource);//CloseHandle
fclose(pFileDest);