Pascal - 文件处理

Pascal文件处理 - 从简单和简单的步骤学习Pascal，从基本概念到高级概念，包括pascal语法，数据类型，全局和局部变量，单位，函数，循环，常量，结构，数组，枚举，集合，记录，文件，变体记录，指针，链接列表和文本处理。

Pascal将文件视为一系列组件，它们必须是统一类型.文件的类型由组件的类型决定.文件数据类型定义为 :

typefile-name = file of base-type;

其中，base-type表示文件组件的类型.除了另一种文件类型之外，基类型可以是整数，实数，布尔，枚举，子范围，记录，数组和集合.使用 var 声明 :

varf1, f2,...: file-name;

以下是定义一些文件类型和文件变量的一些示例 :

type   rfile = file of real;   ifile = file of integer;   bfile = file of boolean;   datafile = file of record   arrfile = file of array[1..4] of integer;var   marks: arrfile;   studentdata: datafile;   rainfalldata: rfile;   tempdata: ifile;   choices: bfile;

创建和写入文件

让我们编写一个程序，为学生的记录创建数据文件.它将创建一个名为students.dat的文件，并将学生的数据写入其中 :

program DataFiles;type   StudentRecord = Record      s_name: String;      s_addr: String;      s_batchcode: String;   end;var   Student: StudentRecord;   f: file of StudentRecord;begin   Assign(f,'students.dat');   Rewrite(f);   Student.s_name := 'John Smith';   Student.s_addr := 'United States of America';   Student.s_batchcode := 'Computer Science';   Write(f,Student);   Close(f);end.

编译运行时，程序会在工作目录中创建一个名为 students.dat 的文件.您可以使用文本编辑器(如记事本)打开文件，查看John Smith的数据.

从文件中读取

我们刚创建并写入名为students.dat的文件中.现在，让我们编写一个程序，从文件中读取学生的数据 :

program DataFiles;type   StudentRecord = Record      s_name: String;      s_addr: String;      s_batchcode: String;   end;var   Student: StudentRecord;   f: file of StudentRecord;begin   assign(f, 'students.dat');   reset(f);    while not eof(f) do      begin      read(f,Student);      writeln('Name: ',Student.s_name);      writeln('Address: ',Student.s_addr);      writeln('Batch Code: ', Student.s_batchcode);   end;      close(f);end.

编译并执行上述代码时，会产生以下结果 :

Name: John SmithAddress: United States of AmericaBatch Code: Computer Science

档案作为子程序参数

Pascal允许文件变量用作标准和用户定义子程序中的参数.以下示例说明了此概念.该程序创建一个名为rainfall.txt的文件，并存储一些降雨数据.接下来，它打开文件，读取数据并计算平均降雨量.

请注意，如果对子程序使用文件参数，则必须将其声明为var参数.

program addFiledata;const   MAX = 4;type   raindata = file of real;var   rainfile: raindata;   filename: string;procedure writedata(var f: raindata);var   data: real;   i: integer;begin   rewrite(f, sizeof(data));   for i:=1 to MAX do      begin      writeln('Enter rainfall data: ');      readln(data);      write(f, data);   end;      close(f);end;procedure computeAverage(var x: raindata);var   d, sum: real;   average: real;begin   reset(x);   sum:= 0.0;   while not eof(x) do      begin      read(x, d);      sum := sum + d;   end;      average := sum/MAX;   close(x);   writeln('Average Rainfall: ', average:7:2);end;begin   writeln('Enter the File Name: ');   readln(filename);   assign(rainfile, filename);   writedata(rainfile);   computeAverage(rainfile);end.

编译并执行上述代码时，会产生以下结果 :

Enter the File Name:rainfall.txtEnter rainfall data:34Enter rainfall data:45Enter rainfall data:56Enter rainfall data:78Average Rainfall: 53.25

文件档案

Pascal中的文本文件由字符行组成，其中每行以行尾标记结束.您可以将这些文件声明并定义为 :

  type  file-name = text;

普通文件和文本文件之间的区别在于文本文件被分成行，每行以特殊的行尾标记结束，由系统自动插入.以下示例创建并写入名为contact.txt : 的文本文件;

program exText;var   filename, data: string;   myfile: text;begin   writeln('Enter the file name: ');   readln(filename);      assign(myfile, filename);   rewrite(myfile);      writeln(myfile, 'Note to Students: ');   writeln(myfile, 'For details information on Pascal Programming');   writeln(myfile, 'Contact: Tutorials Point');   writeln('Completed writing');       close(myfile);end.

编译并执行上述代码时，会产生以下结果 :

Enter the file name:contact.txt Completed writing

附加到文件

附加到文件意味着写入已经包含某些数据的现有文件而不覆盖该文件.以下程序说明了这个 :

program exAppendfile;var   myfile: text;   info: string;begin   assign(myfile, 'contact.txt');   append(myfile);      writeln('Contact Details');   writeln('admin@it1352.com');   close(myfile);      (* let us read from this file *)   assign(myfile, 'contact.txt');   reset(myfile);   while not eof(myfile) do      begin      readln(myfile, info);      writeln(info);   end;   close(myfile);end.

文件处理函数

Free Pascal为文件处理提供以下函数/过程 :

Sr.No.	Function Name & Description
1	procedure Append(var t: Text); Opens a file in append mode
2	procedure Assign(out f: file; const Name:); Assigns a name to a file
3	procedure Assign(out f: file; p: PChar); Assigns a name to a file
4	procedure Assign(out f: file; c: Char); Assigns a name to a file
5	procedure Assign(out f: TypedFile; const Name:); Assigns a name to a file
6	procedure Assign(out f: TypedFile; p: PChar); Assigns a name to a file
7	procedure Assign(out f: TypedFile; c: Char); Assigns a name to a file
8	procedure Assign(out t: Text; const s:); Assigns a name to a file
9	procedure Assign(out t: Text; p: PChar); Assigns a name to a file
10	procedure Assign(out t: Text; c: Char); Assigns a name to a file
11	procedure BlockRead(var f: file; var Buf; count: Int64; var Result: Int64); Reads data from a file into memory
12	procedure BlockRead(var f: file; var Buf; count: LongInt; var Result: LongInt); Reads data from a file into memory
13	procedure BlockRead(var f: file; var Buf; count: Cardinal; var Result: Cardinal); Reads data from a file into memory
14	procedure BlockRead(var f: file; var Buf; count: Word; var Result: Word); Reads data from a file into memory
15	procedure BlockRead(var f: file; var Buf; count: Word; var Result: Integer); Reads data from a file into memory
16	procedure BlockRead(var f: file; var Buf; count: Int64); Reads data from a file into memory
17	procedure BlockWrite(var f: file; const Buf; Count: Int64; var Result: Int64); Writes data from memory to a file
18	procedure BlockWrite(var f: file; const Buf; Count: LongInt; var Result: LongInt); Writes data from memory to a file
19	procedure BlockWrite(var f: file; const Buf; Count: Cardinal; var Result: Cardinal); Writes data from memory to a file
20	procedure BlockWrite(var f: file; const Buf; Count: Word; var Result: Word); Writes data from memory to a file
21	procedure BlockWrite(var f: file; const Buf; Count: Word; var Result: Integer); Writes data from memory to a file
22	procedure BlockWrite(var f: file; const Buf; Count: LongInt); Writes data from memory to a file
23	procedure Close(var f: file); Closes a file
24	procedure Close(var t: Text); Closes a file
25	function EOF(var f: file):Boolean; Checks for end of file
26	function EOF(var t: Text):Boolean; Checks for end of file
27	function EOF: Boolean; Checks for end of file
28	function EOLn(var t: Text):Boolean; Checks for end of line
29	function EOLn: Boolean; Checks for end of line
30	procedure Erase(var f: file); Deletes file from disk
31	procedure Erase(var t: Text); Deletes file from disk
32	function FilePos( var f: file):Int64; Position in file
33	function FileSize(var f: file):Int64; Size of file
34	procedure Flush(var t: Text); Writes file buffers to disk
35	function IOResult: Word; Returns result of last file IO operation
36	procedure Read(var F: Text; Args: Arguments); Reads from file into variable
37	procedure Read(Args: Arguments); Reads from file into variable
38	procedure ReadLn(var F: Text; Args: Arguments); Reads from file into variable and goto next line
39	procedure ReadLn(Args: Arguments); Reads from file into variable and goto next line
40	procedure Rename(var f: file; const s:); Renames file on disk
41	procedure Rename(var f: file; p: PChar); Renames file on disk
42	procedure Rename(var f: file; c: Char); Renames file on disk
43	procedure Rename(var t: Text; const s); Rename file on disk
44	procedure Rename(var t: Text; p: PChar); Renames file on disk
45	procedure Rename( var t: Text; c: Char); Renames file on disk
46	procedure Reset(var f: file; l: LongInt); Opens file for reading
47	procedure Reset(var f: file); Opens file for reading
48	procedure Reset(var f: TypedFile); Opens file for reading
49	procedure Reset(var t: Text); Opens file for reading
50	procedure Rewrite(var f: file; l: LongInt); Opens file for writing
51	procedure Rewrite(var f: file); Opens file for writing
52	procedure Rewrite(var f: TypedFile); Opens file for writing
53	procedure Rewrite(var t: Text); Opens file for writing
54	procedure Seek(var f: file; Pos: Int64); Sets file position
55	function SeekEOF(var t: Text):Boolean; Sets file position to end of file
56	function SeekEOF: Boolean; Sets file position to end of file
57	function SeekEOLn(var t: Text):Boolean; Sets file position to end of line
58	function SeekEOLn: Boolean; Sets file position to end of line
59	procedure SetTextBuf(var f: Text; var Buf); Sets size of file buffer
60	procedure SetTextBuf(var f: Text; var Buf; Size: SizeInt); Sets size of file buffer
61	procedure Truncate(var F: file); Truncate the file at position
62	procedure Write(Args: Arguments); Writes variable to file
63	procedure Write(var F: Text; Args: Arguments); Write variable to file
64	procedure Writeln(Args: Arguments); Writes variable to file and append newline
65	procedure WriteLn(var F: Text; Args: Arguments); Writes variable to file and append newline