檔案讀寫與例外處理 (File IO and Exception Handling)

檔案讀寫與例外處理 (File IO and Exception Handling)
鄭士康國立台灣大學電機工程學系/電信工程研究所/ 資訊網路與多媒體研究所

綱要簡易檔案讀寫錯誤代碼例外物件、try、catch、finally 自訂例外例外類別的階層結構巢狀try與catch 檔案類別
物件序列化

加入文字檔專案/加入新項目/文字檔/名稱/加入鍵入資料檔案/另存***為. . . 檢查儲存位置

串流(Stream)的觀念 StreamReader 輸入檔 Heap 記憶區 StreamWriter 輸出檔

FileDemo.Program (1/6) /* * 示範文字檔案之讀寫 * skj 4/20/2007 *
* 假設欲讀入之資料檔格式如下: * 第一列為一個整數代表以下每列有多少個整數數據 * 欲寫出之資料檔格式與欲讀入之資料檔格式相似 * 測試: * 欲讀入之資料檔檔名為Test.dat * 欲寫出之資料檔檔名為Test.output

FileDemo.Program (2/6) * 欲讀入之資料檔內容為(數據之間以一個空白隔開) * 3 * 1 4 2 * 2 3 5
* 7 6 9 * * * * 寫出之資料檔內容相同, 但數據之間以TAB('\t')分開, 即 * * * * *

FileDemo.Program (3/6) * 注意如果執行偵錯版本, 所用資料檔要放在專案的bin\Debug * 檔案夾,
* 如果不偵錯, 須放在bin\Release檔案夾, 否則檔案名要用完整 * 檔案路徑 */ using System; using System.IO; namespace FileDemo { class Program static void Main(string[] args)

FileDemo.Program (4/6) Console.Write("輸入欲讀入之資料檔名: ");
string fileName = Console.ReadLine(); StreamReader input = new StreamReader(fileName); Console.Write("輸入欲寫出之資料檔名: "); fileName = Console.ReadLine(); StreamWriter output = new StreamWriter(fileName); string line; string[] head = new string[2]; // 讀入並寫出第一列 line = input.ReadLine(); int nDataPerLine = int.Parse(line); output.WriteLine(nDataPerLine);

FileDemo.Program (5/6) // 讀入並寫出後續數據 string[] dataString = new
string[nDataPerLine]; int data; while (!input.EndOfStream) { line = input.ReadLine(); dataString = line.Split(' '); for ( int i = 0; i < nDataPerLine; ++i) data = int.Parse(dataString[i]); Console.Write(data + "\t"); output.Write(data + "\t"); }

FileDemo.Program (6/6) Console.WriteLine(); output.WriteLine(); }
output.Close(); input.Close();

練習產生一文字資料檔，在其中用星號*和空白製作圖案撰寫程式讀取此一資料檔，並在螢幕印出其中圖案

範例問題假設有一N_ROW列、N_COL欄的整數表格，寫一程式計算每列總和、每欄總和、及全部總和。以如下2列3欄表格為例(Case 1)：
其每列總和為 9、18，每欄總和為8、11、8，全部總和為27。利用一個二維陣列儲存表格資料，兩個一維陣列分別儲存每列總和及每欄總和。 3 4 2 5 7 6

資料檔格式 2, 3 3, 4, 2 5, 7, 6 i.e., <nRow>, <nCol>
<data[0,0]>, <data[0,1]>, . . ., <data[0,nCol]> . . . <data[nRow,0]>, <data[nRow,1]>, . . ., <data[nRow, nCol]>

TableDemo.Program片段 using System; using System.Diagnostics;
namespace TableDemo { class Program static void Main(string[] args) Debug.Assert(TableTest.Case1_OK(), "Table test: Case 1 failed"); }

TableDemo.TableTest 片段
public static bool Case1_OK() { Table table = new Table("Test1.dat"); int[] rowSum = table.RowSum(); Debug.Assert(rowSum[0] == 9); Debug.Assert(rowSum[1] == 18); int[] colSum = table.ColSum(); Debug.Assert(colSum[0] == 8); Debug.Assert(colSum[1] == 11); Debug.Assert(colSum[2] == 8); Debug.Assert(table.TotalSum() == 27); return true; }

TableDemo.Table 片段(1/6) private int nRow; private int nCol;
private int[,] data; public Table(string fileName) { StreamReader input = new StreamReader(fileName); string line; string[] head = new string[2]; line = input.ReadLine(); head = line.Split(','); nRow = int.Parse(head[0]); nCol = int.Parse(head[1]); data = new int[nRow, nCol];

TableDemo.Table 片段(2/6) int i; int j; for (i = 0; i < nRow; ++i) {
string[] dataString = new string[nCol]; int i; int j; for (i = 0; i < nRow; ++i) { line = input.ReadLine(); dataString = line.Split(','); for (j = 0; j < nCol; ++j) data[i,j] = int.Parse(dataString[j]); }

TableDemo.Table 片段(3/6) public int[] RowSum() {
int[] rowSum = new int[nRow]; for (int i = 0; i < nRow; ++i) rowSum[i] = 0; for (int j = 0; j < nCol; ++j) rowSum[i] += data[i, j]; } return rowSum;

TableDemo.Table 片段(4/6) public int[] ColSum() {
int[] colSum = new int[nCol]; for (int j = 0; j < nCol; ++j) colSum[j] = 0; for (int i = 0; i < nRow; ++i) colSum[j] += data[i, j]; } return colSum;

TableDemo.Table 片段(5/6) public int TotalSum() { int totalSum = 0;
for (int i = 0; i < nRow; ++i) for (int j = 0; j < nCol; ++j) totalSum += data[i, j]; } return totalSum;

練習在類別Table中增加建構式public Table(int[,] data) ，以便由一個矩形陣列建立表格
在類別TableTest中增加public static bool Case2_OK() ，以測試上述建構式修改主程式，進行測試

物件序列化

錯誤代碼應用例虛擬碼(1/3) readFile { openFile; determineSize; allocateMemory;
readFileIntoMemory; closeFile; } *吳瑞千譯, W. D. Mitchell原著, JAVA 程式疑難排解, 麥格羅希爾, 2001, pp. 3-8 ~3-10.

錯誤代碼應用例虛擬碼(2/3) errorCodeType readFile { initialize errorCode = 0;
openFile; if( fileIsOpen ) { determineSize; if( gotFileLength ) { allocateEnoughMemory; if( memoryAllocated ) { readFileIntoMemory; if( readFailed ) { errorCode = -1; handleError; } else { errorCode = -2; handleError; }

錯誤代碼應用例虛擬碼(3/3) } else { errorCode = -3; handleError; } closeFile;
if( fileDidNotClose && errorCode == 0 ) { errorCode = -4; handleError; errorCode = -5; handleError; return errorCode;

Try-Catch 應用例虛擬碼(1/2) readFile { try { openFile; determineSize;
allocateMemory; readFileIntoMemory; closeFile;

Try-Catch 應用例虛擬碼(2/2) } catch( fileDidNotOpen ) {
handleError; // or throwException } catch( sizeNotDetermined ) { } catch( memoryAllocationFailed ) { } catch( couldNotReadFile ) { } catch( couldNotCloseFile ) { }

例外處理優點分離正常與錯誤處理程式碼，易於了解及偵錯例外物件包含所需清楚資訊，減輕記憶負擔，易於使用
易於繼承衍生例外物件，減少所需重複程式碼

物件序列化

UsingTryCatch.Program (1/3)
/* * 示範try...catch之使用 * 5/14/2007 */ using System; namespace UsingTryCatch { class Program static void Main(string[] args)

{ Console.Write("輸入除數: "); int number = int.Parse(Console.ReadLine()); int result = 5 / number; } catch (Exception e) Console.WriteLine("發生例外"); Console.WriteLine("例外原因: " + "\n\n" + e.Message + "\n"); Console.WriteLine("擲出例外之方法的呼叫堆疊: " + "\n\n" + e.StackTrace + "\n");

Console.WriteLine("擲出例外之地點: " + "\n\n" + e.TargetSite + "\n"); Console.WriteLine( "擲出例外之程式物件來源: " + "\n\n" + e.Source + "\n"); Console.WriteLine("例外之相關細節: " + "\n\n" + e.ToString() + "\n"); }

UsingTryCatch2.Program (1/3)
/* 捕捉不同例外 * 5/14/2007 */ using System; namespace UsingTryCatch2 { class Program static void Main(string[] args) bool success = false; do try

Console.Write("輸入除數: "); int number = int.Parse(Console.ReadLine()); int result = 5 / number; Console.WriteLine("除結果為" + result); success = true; } catch (FormatException e) { Console.WriteLine("請輸入數值"); Console.WriteLine(e.Message); catch (DivideByZeroException e) Console.WriteLine("不可除以零");

catch (Exception e) { Console.WriteLine("其他錯誤"); Console.WriteLine(e.Message); } finally if (!success) Console.WriteLine("再試一次"); } while (!success);

練習參考FileDemo程式，寫一程式打開一不存在之資料檔，觀察會有何例外發生修改程式catch此例外，印出訊息後結束程式執行

物件序列化

UserDefinedException.Program (1/5)
/* * 示範使用者自訂例外之使用 * 5/22/2010 */ using System; namespace UserDefinedException { class Program static void Main(string[] args) int nStudents = 3;

Student[] table = new Student[nStudents]; try { table[0] = new Student("B645330", 90); Console.WriteLine("table[0] = {0} : {1}", table[0].RegNo, table[0].Grade); table[1] = new Student("B645331", 102); //table[1] = new Student("B645331", 100); Console.WriteLine("table[1] = {0} : {1}", table[1].RegNo, table[1].Grade); table[2] = new Student("B645332", 55); Console.WriteLine("table[2] = {0} : {1}", table[2].RegNo, table[2].Grade); //Console.WriteLine("table[3] = {0} : {1}", // table[3].RegNo, table[3].Grade); }

catch (GradeOutOfRangeException e) { Console.WriteLine(e); } catch (IndexOutOfRangeException e) Console.WriteLine(e.Message); catch (Exception e)

class Student { private string regNo; private int grade; public Student(string regNo, int grade) { if (grade < 0 || grade > 100) throw new GradeOutOfRangeException( regNo, grade); this.regNo = regNo; this.grade = grade; } public string RegNo { get { return regNo; } public int Grade { get { return grade; }

class GradeOutOfRangeException : ApplicationException { private string message; public GradeOutOfRangeException( string regNo, int grade) : base() message = "學生" + regNo + "之分數" + grade + "不在0與100之間"; } public override string ToString() return message;

物件序列化

例外類別階層 Exception ApplicationException SystemException
ArithmeticException DivideByZeroException NotFiniteNumberException OverflowException FormatException InvalidCastException IndexOutOfRangeException NullReferenceException StackOverflowException IOException

練習撰寫類別Square，模擬邊長為a的正方形。在以a為輸入參數之建構式中檢驗a是否為正，若否則throw一自訂之例外物件
撰寫此一自定之例外類別撰寫測試程式，嘗試建立邊長為-1的正方形，並catch例外，輸出訊息後結束

物件序列化

NestedTryAndCatch.Program(1/7)
/* * 示範巢狀try...catch敘述之使用 * 5/22/2010 */ using System; namespace NestedTryAndCatch { class Program static void Main(string[] args) int nStudents = 1; bool validNStudents = false;

do { Console.Write("輸入學生人數: "); try nStudents = int.Parse(Console.ReadLine()); if (nStudents > 0) validNStudents = true; } catch (FormatException e) Console.WriteLine(e.Message); catch (Exception e) } while (!validNStudents);

{ Student[] table = new Student[nStudents]; for (int i = 0; i < nStudents; ++i) bool validGrades = false; do Console.WriteLine("輸入第" + (i + 1) + " 個學生學號及成績, 以一個空白分隔: "); string line; string[] data = new string[2]; line = Console.ReadLine(); data = line.Split(' ');

string regNo = data[0]; int grade = Convert.ToInt32(data[1]); table[i] = new Student(regNo, grade); Console.WriteLine( "table[" + i + "] = {0} : {1}", table[i].RegNo, table[i].Grade); validGrades = true; } catch (GradeOutOfRangeException e){ Console.WriteLine(e); catch (FormatException e) { Console.WriteLine(e.Message); } while (!validGrades);

catch (IndexOutOfRangeException e) { Console.WriteLine(e.Message); } catch (Exception e)

class Student { private string regNo; private int grade; public Student(string regNo, int grade) { if (grade < 0 || grade > 100) throw new GradeOutOfRangeException( regNo, grade); this.regNo = regNo; this.grade = grade; } public string RegNo { get { return regNo; } public int Grade { get { return grade; }

class GradeOutOfRangeException : ApplicationException { private string message; public GradeOutOfRangeException(string regNo, int grade) : base() message = "學生" + regNo + "之分數" + grade + "不在0與100之間"; } public override string ToString() return message;

練習將NestedTryAndCatch程式改為由資料檔讀取資料，注意catch檔案不存在的例外狀況
測試一錯誤資料檔，使程式提早遇到End Of File的情況，觀察有何例外發生修改程式，使能處理End Of File的情況

物件序列化

串流(Stream) 檔案程式變數位元組串流 Test.dat 程式變數位元組串流網路接口 (Socket)

程式執行時自動產生的串流物件類別Console的三個相關資料成員 Console.In Console.Out Console.Error
連接至鍵盤，標準輸入串流物件用於Console函式Read與ReadLine Console.Out 連接至螢幕，標準輸出串流物件用於Console函式Write與WriteLine Console.Error 連接至螢幕，標準錯誤訊息輸出串流物件

命名空間System.IO

System.IO中的類別 StreamReader StreamWriter FileStream MemoryStream
自檔案輸入文字 StreamWriter 輸出文字至檔案 FileStream 輸入及輸出至檔案均可能 MemoryStream BufferedStream

物件序列化

物件序列化(Serialization)與去序列化(Deserialization)
利用BinaryFormatter，在Stream進行序列化將物件轉換為適當格式之資料，寫入檔案去序列化自檔案以適當格式讀出資料，重建物件

UsingSerialization.Program (1/8)
/* * 以類別Student及GraduateStudent說明物件的序列化與 * 去序列化 * 5/22/2010 */ using System; using System.IO; using System.Runtime.Serialization; using System.Runtime.Serialization.Formatters.Binary; using System.Diagnostics; namespace UsingSerialization { [Serializable] class Student private string regNo; private string name;

public Student() { regNo = ""; name = ""; } public Student(string regNo, string name){ this.regNo = regNo; this.name = name; public string RegNO { get { return regNo; } public string Name { get { return name; }

[Serializable] class GraduateStudent : Student { private string advisor; public GraduateStudent() : base() { advisor = ""; } public GraduateStudent( string regNo, string name, string advisor) : base(regNo, name) { this.advisor = advisor; public string Advisor { get { return advisor; }

class Program { static void Main(string[] args) Student so1 = new Student( "B645331", "Thomas"); GraduateStudent so2 = new GraduateStudent( "F685329", "Richard", "Aaron"); BinaryFormatter formatter = new BinaryFormatter(); try { FileStream output = new FileStream("Test.dat", FileMode.Create, FileAccess.Write);

formatter.Serialize(output, so1); formatter.Serialize(output, so2); output.Close(); } catch (SerializationException) { Console.WriteLine( "Error writting to file in output"); catch (IOException) "Can not create or close file for output"); try

FileStream input = new FileStream("Test.dat", FileMode.Open, FileAccess.Read); try { while (true) Object obj = formatter.Deserialize(input); if ( obj.GetType() == so1.GetType()) Student si = (Student)obj;

Console.WriteLine( si.RegNO + "\t" + si.Name ); } else if (obj.GetType() == so2.GetType()) { GraduateStudent si = (GraduateStudent)obj; Console.WriteLine( si.RegNO + "\t" + si.Name + "\t" + si.Advisor); else { throw new SerializationException();

catch (SerializationException) { // close stream if no data left input.Close(); } catch (IOException) { Console.WriteLine( "Can not close file for input"); catch (FileNotFoundException) { "Can not open file in building intput");

檔案讀寫與例外處理 (File IO and Exception Handling)

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