¶Code Complete II《軟體建構之道 2》#9 讀書心得與整理

原文連結: https://darkblack01.blogspot.com/2013/03/code-complete-ii-29.html
移植時的最後更新日期: 2013-03-28T13:44:04.383+08:00

第九章 虛擬碼程式設計流程
The Pseudocode Programming Process

9.1 構築類別及常式
Summary of Steps in Building Classes and Routines

構築類別的步驟
Steps in Creating a Class

建立常式的步驟
Steps in Building a Routine

9.2 虛擬碼的優點
Pseudocode for Pros

•   精確的說明特定的行為
•   避免使用程式語言的元素。虛擬碼讓你可以在略高於程式碼本身的層次進行設計
•   描述實現的目標，而非實現的語法
•   記載低層次的目標，降低產生程式碼的難度，提高程式碼實現的易錯或矛盾之處。

Example of Bad Pseudocode
increment resource number by 1
allocate a dlg struct using malloc
if malloc() returns NULL then return 1
invoke OSrsrc_ini 109 t to initialize a resource for the operating system
*hRsrcPtr = resource number
return 0

Example of Good Pseudocode
Keep track of current number of resources in use
If another resource is available
 Allocate a dialog box structure
 If a dialog box structure could be allocated
  Note that one more resource is in use
  Initialize the resource
  Store the resource number at the location provided by the caller
 Endif
Endif
Return TRUE if a new resource was created; else return FALSE

9.3 使用PPP構築常式
Constructing Routines Using the PPP

1.   設計常式
2.   撰寫常式
3.   檢查程式碼
4.   清除零星問題
5.   視需要重覆

設計常式
Design the routine

輸入: error code
輸出: error code對應的error message。
還可以處理無效的錯誤碼。

如果程式是以互動式介面（視窗介面環境）執行:
那ReportErrorMessage()需要向用戶顯示錯誤訊息；

如果程式是以command line環境執行:
那ReportErrorMessage()應把錯誤訊息記錄在一個訊息文件裡。在輸出錯誤訊息之後，ReportErrorMessage()返回一個狀態值，表示其操作是成功還是失敗。

高層級設計必須能指示以下的項目：

•     常式要隱藏的資訊
•     常式的輸入
•     常式的輸出
•     在常式受到呼叫前，可確定的前置條件（防火牆）
•     將控制權回傳呼叫者後，可確定的後置條件（防火牆）

以下是ReportErrorMessage()考量的方式:

•   常式隱藏兩項事實:
1. error message的文字
2. 目前處理方法（無論是互動列還是command line）
•   常式沒有確定的前置條件
•   常式的輸入是error code
•   兩種輸出會受到呼叫:
1. error message
2. status, ReportErrorMessage() return的值。
•   常式保證狀態值是「成功」或「失敗」

//常式標題虛擬碼
This routine outputs an error message based on an error code
supplied by the calling routine. The way it outputs the message
depends on the current processing state, which it retrieves
on its own. It returns a value indicating success or failure.
//常式內部行為虛擬碼
set the default status to "fail"
look up the message based on the error code

if the error code is valid
  if doing interactive processing, display the error message interactively and declare success

  if doing command line processing, log the error message to the command line and declare success

if the error code is not valid, notify the user that an internal error
has been detected

return status information

• 設計→概述→角色→常式

撰寫常式
Code the routine

/*
This routine outputs an error message based on an error code
supplied by the calling routine. The way it outputs the message
depends on the current processing state, which it retrieves
on its own. It returns a value indicating success or failure.
*/
//新增這一個常式宣告
Status ReportErrorMessage(
ErrorCode errorToReport
)

set the default status to "fail"
look up the message based on the error code

if the error code is valid
  if doing interactive processing, display the error message interactively and declare success

  if doing command line processing, log the error message to the command line and declare success

if the error code is not valid, notify the user that an internal error
has been detected

return status information

/*
This routine outputs an error message based on an error code
supplied by the calling routine. The way it outputs the message
depends on the current processing state, which it retrieves
on its own. It returns a value indicating success or failure.
*/
//新增這一個常式宣告
Status ReportErrorMessage(
ErrorCode errorToReport
)
{
  //set the default status to "fail"
  //look up the message based on the error code

  //if the error code is valid
    //if doing interactive processing, display the error message interactively and declare success

    //if doing command line processing, log the error message to the command line and declare success

  //if the error code isn't valid, notify the user that an internal error
  //has been detected

  //return status information
}

/*
This routine outputs an error message based on an error code
supplied by the calling routine. The way it outputs the message
depends on the current processing state, which it retrieves
on its own. It returns a value indicating success or failure.
*/
//新增這一個常式宣告
Status ReportErrorMessage(
ErrorCode errorToReport
)
{
    //set the default status to "fail"
    Status errorMessageStatus = Status_Failure;
    //look up the message based on the error code
    Message errorMessage = LookupErrorMessage( errorToReport );

    //if the error code is valid
    if ( errorMessage.ValidCode() )
    {
        // determine the processing method →在此新增的
        ProcessingMethod errorProcessingMethod = CurrentProcessingMethod();
        //if doing interactive processing, display the error message interactively and declare success
        if ( errorProcessingMethod == ProcessingMethod_Interactive )
        {
            DisplayInteractiveMessage( errorMessage.Text() );
            errorMessageStatus = Status_Success;
        }
        //if doing command line processing, log the error message to the command line and declare success
        else if ( errorProcessingMethod == ProcessingMethod_CommandLine )
        {
            CommandLine messageLog;
            if ( messageLog.Status() == CommandLineStatus_Ok )
            {
                messageLog.AddToMessageQueue( errorMessage.Text() );
                messageLog.FlushMessageQueue();
                errorMessageStatus = Status_Success;
            }
        }
    }
    //if the error code isn't valid, notify the user that an internal error has been detected
    else
    {
        DisplayInteractiveMessage("Internal Error: Invalid error code in ReportErrorMessage()");
    }
  //return status information
  return errorMessageStatus;
}

檢查程式碼
Check the code

• desk checking
• peer review
• walkthrough
• inspection

• 程式碼出錯原因機率分佈: 
硬體、編譯器、作業系統: 5%
程式碼的問題: 95%

1. 將編譯器設定成最挑剔的等級
2. 使用驗證工具(validators)
3. 消除警告的原因

收拾殘局
Clean up leftovers

視需要重覆步驟
Repeat as needed

9.4 PPP的替代方法
Alternatives to the PPP