在C++程序中添加邏輯流程控制

問(wèn)題的引出
    在計(jì)算機(jī)程序中，除了常見的執(zhí)行流程控制，還有邏輯流程控制；有時(shí)，執(zhí)行流程即為邏輯流程，但在大多數(shù)情況下還是有所區(qū)別的，例如，假定有一個(gè)Web服務(wù)器使用同步套接字讀取HTTP請(qǐng)求，那么會(huì)編寫如下的代碼：
    void read(HTTP_REQUEST& http_request)
    {
    read(http_request.header);
    read(http_request.body, http_request.header);
    }
    void read(HTTP_REQUEST_HEADER& header)
    {
    string line = read_line();
    parse_request_link(line, header.method, header.uri,
    header.version);
    while (TRUE)
    {
    line = read_line();
    if (line.empty())
    break;
    parse_header_field(line, header);
    }
    }
    void read(BYTE[]& body, HTTP_REQUEST_HEADER& header)
    {
    string transfer_encoding = header.fields['Transfer-Encoding'];
    if (transfer_encoding != b.chunkedb.)
    body = read_bytes(header.fields['Content-Length']);
    else
    {
    while (TRUE)
    {
    string chunk_header = read_line();
    DWORD chunk_size = atoi(chunk_header);
    if (chunk_size == 0)
    break;
    BYTE[] chunk_body = read_bytes(chunk_size);
    body += chunk_body;
    }
    }
    }
    string read_line()
    {
    while (TRUE)
    {
    int n = strpos(read_buffer, b.\nb., read_buffer.size());
    if (n > 0)
    break;
    read_buffer += socket.read();
    }
    return read_buffer.extract(n);
    }
    Byte[] read_bytes(int sz)
    {
    while (TRUE)
    {
    if (sz <= read_buffer.size())
    break;
    read_buffer += socket.read();
    }
    return read_buffer.extract(sz);
    }
    在這段代碼中，執(zhí)行流程與邏輯流程是一致的，然而，如果在那些被動(dòng)接收事件的場(chǎng)合使用了異步套接字，就必須編寫下面這樣的代碼了：
    read()
    {
    read_buffer += socket.read();
    if (state == read_request_line)
    {
    if (!read_line(line))
    return;
    parse_request_link(line, method, uri, version);
    state = read_header_field;
    }
    while (state == read_request_line)
    {
    if (!read_line(line))
    return;
    if (line.empty())
    {
    transfer_encoding = header.fields['Transfer-Encoding'];
    if (transfer_encoding != b.chunkedb.)
    {
    content_length = header.fields['Content-Length'];
    state = read_body;
    }
    else
    state = read_chunk_header;
    }
    else
    parse_header_field(line, header, value);
    }
    if (state == read_body)
    {
    request_body += read_buffer;
    read_buffer.clear();
    if (request_body.size() >= content_length)
    state = read_finished;
    return;
    }
    if (state == read_chunk_header)
    {
    if (!read_line(line))
    return;
    chunk_size = atoi(line);
    if (chunk_size == 0)
    {
    state = read_finished;
    return;
    }
    state = read_body;
    }
    if (state == read_chunk_body)
    {
    request_body.append(read_buffer, chunk_size);
    if (chunk_size == 0)
    state = read_chunk_header;
    return;
    }
    }
    執(zhí)行流程完全不同了，但邏輯流程卻仍保持不變，因?yàn)橹荒芤粔K一塊地接收數(shù)據(jù)，還必須保存狀態(tài)值及其他變量，以便在事件發(fā)生時(shí)進(jìn)行相應(yīng)的處理。以上只是一些示范性代碼，并不能真正工作，在實(shí)際中要編寫像這樣的函數(shù)會(huì)更加復(fù)雜，也更加容易出錯(cuò)