(1) Using function "freopen" (reopen stream with different files or modes) in "stdio.h" can easily read the data in a file.

// Below gives an example in C++ Builder

// "in.txt" is a text file with the same folder of ~.exe as follows: 
//  5 6
//  0 0 0 0 0 0
//  0 1 1 1 1 0
//  0 1 1 1 1 0
//  0 1 1 1 1 0
//  0 0 0 0 0 0

#include <stdio.h>

#include <vcl.h>

#pragma hdrstop

#include "Unit1.h"

//---------------------------------------------------

#pragma package(smart_init)

#pragma resource "*.dfm"

using namespace std;  
// Add this statement for using "cin/cout" 

TForm1 *Form1;

//----------------------------------------------------

__fastcall TForm1::TForm1(TComponent* Owner): TForm(Owner)

{

}

//----------------------------------------------------

void __fastcall TForm1::Button1Click(TObject *Sender)

{   int m, n, i, j;
    freopen("in.txt", "r", stdin);
    // read data in "in.txt" as standard input 將in.txt當成stdin
    freopen("out.txt", "w", stdout);  // write into file "out.txt"
    cin >> m >> n;  // get the matrix size m*n from in.txt (stdin)
    int ** maze;
    maze = new int * [m];
    for (int i=0; i<m; i++)
    {    maze[i] = new int [n];
for (int j=0; j<n; j++)
    cin >> maze[i][j];  // 自in.txt (stdin) 讀資料
    }
    fclose(stdin);
    cin.clear();  // clear the possible errors from cin  
    String s;  // write data onto Form1
    for (int i=0; i<m; i++)
    {   for (int j=0, s=""; j<n; j++)
        s = s + IntToStr(maze[i][j]) + " ";
        Form1->Memo1->Lines->Add(s);
    }
    // write data into file "out.txt"
    cout << m << " " << n << endl;
    for (i=0; i<m; i++)
    {   for (j=0; j<n; j++)
            cout << maze[i][j] <<" ";
cout << endl;
    }
    fclose(stdout);
}
// Refer to https://en.cppreference.com/w/cpp/io/c/freopen

(2.1) In C++Builder, please drag-&-drop "OpenDialog" object into Form first, which lead you to read a file from the disk.

// 將檔案內容(含兩整數m,n和 m*n 個整數)讀入程式中 (BCB)：

#include "stdio.h"

//----------------------------------------------------------

#pragma package(smart_init)

#pragma resource "*.dfm"

TForm1 *Form1;

//-----------------------------------------------------------

__fastcall TForm1::TForm1(TComponent* Owner): TForm(Owner)

{

}

//-------------------------------------------------------------

int maze [20][20];

void __fastcall TForm1::Button1Click(TObject *Sender)

{     FILE *fp; // Define fp as a pointer pointing to some file (with data type FILE) in HD

 String out;  

 int m, n, i, j;

 AnsiString infile;   // Use builder's string (AnsiString) to ease the conversion (into const char *)

 if (OpenDialog1->Execute())

 {   infile = OpenDialog1->FileName;

   fp = fopen(infile.c_str(), "r+");

        //c_str函数的傳回值是 const char *, 即把AnsiString轉成const char *給fopen使用

  fscanf(fp, "%d %d", &m, &n);    // Read in two integers m & n

  Memo1->Lines->Add("(m, n)="+IntToStr(m)+", "+IntToStr(n));

  for (i=0; i<m; i++)    // Reda in m*n 0/1/2's into maze[][]

   for (j=0; j<n; j++)

    fscanf(fp, "%d", &maze[i][j]);

  fclose(fp);

  for (i=0; i<m; i++)      // Print out maze[][] in Memo1

  {  out = "";

   for (j=0; j<n; j++) out += "  "+IntToStr(maze[i][j]);

   Memo1->Lines->Add(out);

  }

  // Print out maze[][] in StringGrid1

  StringGrid1->RowCount = m;

  StringGrid1->ColCount = n;

  for (i=0; i<m; i++)

     for (j=0; j<n; j++)

     StringGrid1->Cells[j][i] = maze[i][j];

  }

 }

--- An example for (m, n) = (4, 4) where (0, 0) is the entrance and (m, n) = (4, 4) is the exit -----------

4 4

0 1 1 0

0 0 1 1

1 0 0 1

1 1 1 0

--- An example for (m, n) = (7, 7) where (1, 1) is the entrance and (m-1, n-1) = (6, 6)  is the exit ((1,0)-(1,1) and (6,6)-(6,7) are intentionally set as parts of the tour so that the final tour would be  (1,0)-(1,1)- ... -(6,6)-(6,7)) -----------

7 7

2 2 2 2 2 2 2

0 0 0 0 1 1 2

2 0 1 0 0 0 2

2 0 1 1 1 0 2

2 0 0 1 1 0 2

2 1 0 0 0 0 0

2 2 2 2 2 2 2

//------------寫檔範例--------------

if (SaveDialog1->Execute())     //確認SaveDialog1讀取檔案成功

{ // 取SaveDialog1所開啟的檔案名稱, 將檔案名稱轉為char格式後用fopen開啟此檔案

   AnsiString file_name = SaveDialog1->FileName;

   FILE *fp = fopen(file_name.c_str(),"w");  // "w" 表示開以寫檔的方式開啟

   //利用fprintf將g_matrix中的元素寫入fp, 當需要換行時使用putc將'\n'加入fp中

   if (fp)

    {   fprintf(fp, "%d %d", g_Heigh, g_Width);

        putc('\n', fp);

        for  (int i=0 ; i<g_Heigh ; i++)

        {      for (int j=0 ; j<g_Width ; j++)

               {    fprintf(fp, "%d ", g_maze[i][j]);

                }

                putc('\n', fp);

        }

        fclose(fp);   // 寫完檔後請關檔

   }

}

使用 Builder 者，不必參閱下面資料！

(2.2) 將檔案內容當整數讀入程式中 (VisualStudio C++)：

-------------- 利用 stdio.h 的指令 --- 讀檔 --- 寫檔 ------------------ 

# include <stdio.h>

(or # include <iostream>)

// 欲使用檔案功能, 請 include stdio.h 或 iostream 擇一即可

using namespace System::Runtime::InteropServices;

// 呼叫 Marshal::StringToHGlobalAnsi 轉換 String ^ to char * 時用!

// 下面的 fopen 需要檔名以 char * 型態為參數

// 有關 字串轉換 ==> https://support.microsoft.com/zh-tw/kb/311259

String ^ a;

String ^ b;

int m, p;

char * fname;

if (openFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK) // 順利開啟檔案才繼續往下做

{  a = openFileDialog1->FileName;

   char * str2 = (char*) (void*) Marshal::StringToHGlobalAnsi(a);

   FILE *fp = fopen(str2,"r"); // 讀檔, 注意第二參數為 "r" (read) 

   if (fp)

   {  fscanf(fp, "%d %d", &m, &p); 

      listBox1->Items->Add("m="+m+" p="+p); 

      listBox1->Items->Add(a); 

      fclose(fp);   // 讀完檔後請關檔

   } 

   // 下面程式碼將檔名 xxx.yyy 變更為 xxx-1.yyy 做為寫入檔案的檔名

   int k = a->IndexOf(".");

   b = a->Substring(0, k)+"-1"+a->Substring(k, a->Length-k);

   str2 = (char*)(void*)Marshal::StringToHGlobalAnsi(b);

   listBox1->Items->Add(b);

   fp = fopen(str2,"w");  // 寫檔, 注意第二參數為 "w" (write)

   if (fp) 

   {  fprintf(fp, "m=%d p=%d", m, p); 

      putc('\n', fp); 

      fclose(fp);      // 寫完檔後務必關檔

   }

   fp = fopen(str2,"a");  // 自檔尾寫入, 注意第二參數為 "a" (append)

   if (fp)

   {  fprintf(fp, "append=> m=%d p=%d", m, p); 

      fclose(fp);      // 寫完檔後務必關檔  

   }

}

------------------------ 與 Mouse in a Maze 有關 -----------------------

--------- Read in a maze from a file as above and Show it in dataGridView ------ using String ^ (VS C++) ---

private: System::Void button4_Click(System::Object^  sender, System::EventArgs^  e) 

{   // wchar_t chrow[256], cm[10], cp[10]; //String ^ S, ^ T, ^ U = "";

    String ^ S;

    int m, p, i, j, p1, p2, len;

    if (openFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK) // 順利開啟檔案才繼續往下做

    { richTextBox1->LoadFile(openFileDialog1->FileName, RichTextBoxStreamType::PlainText);

S = richTextBox1->Lines[0];

p1 = S->IndexOf(" ");

m = int::Parse(S->Substring(0, p1));

p = int::Parse(S->Substring(p1+1, S->Length-p1-1));

     maze = new int * [m];

for (i=0; i<m; i++)

{ maze[i] = new int [p];

}

for (i=1; i<=m; i++)

{   S = richTextBox1->Lines[i];

    for (j=0; j<p; j++)

    maze[i-1][j] = int::Parse(S->Substring(2*j, 1));

}

dataGridView1->RowCount = m;                // Define the size of dataGridView1

dataGridView1->ColumnCount = p;

dataGridView1->ColumnHeadersVisible = false;

dataGridView1->RowHeadersVisible = false;   // Remove the Row/ColumnHeader 

for (i=0; i<m; i++)

{   // dataGridView1->Columns[i]->Width = 80;

    // dataGridView1->Rows[i]->Height = 80;

    for (j=0; j<p; j++)

    { if (maze[i][j] == 2)

    // dataGridView1->Rows[i]->Cells[j]->Value =  "●";

    dataGridView1->Rows[i]->Cells[j]->Style->BackColor = Color::Olive; // Beige; //IndianRed;

else 

    // dataGridView1->Rows[i]->Cells[j]->Value =  maze[i][j];

    if (maze[i][j] == 1) 

dataGridView1->Rows[i]->Cells[j]->Style->BackColor = Color::DarkKhaki; //LightGray              else dataGridView1->Rows[i]->Cells[j]->Style->BackColor = Color::Ivory; //象牙色;

    }  

}

for (i=0; i<m; i++)

{    delete maze[i];

}

delete maze;

    }

}

-------------------------------------------------------------------------------------------

將檔案內容當串流(stream)讀讀入程式中 (VisualStudio C++)：

using namespace System::IO;

using namespace System::Text; 

// 呼叫StreamReader與StreamWriter用

if(openFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK)  // 順利開啟檔案才繼續往下做

{

     // 讀檔

    StreamReader^ file = gcnew StreamReader(openFileDialog1->FileName); 

    String^ one_line = file->ReadLine(); // 一次讀檔案中的一列

    cli::array<String^>^ split = one_line->Split(' ');

    // 以空白當作分隔符號抓取每兩個空白間的字串

    /*

    例如：

    檔案中的第一列串流是 Data Structures and Algorithms

    我們以空白字元當分隔符號去分隔第一列串流

    就能分別擷取出Data, Structures, and, Algorithms這四個字串

    */

    // 寫檔

    StreamWriter^ output = gcnew StreamWriter(Directory::GetCurrentDirectory()+" - output.txt");

    // 必須給系統知道寫檔的檔名與存放路徑

    for(i=0; i< dataGridView1->RowCount; i++)

    {

        String^ forOutput = "";

        for(j=0; j<dataGridView1->ColumnCount; j++)

        {

            forOutput += dataGridView1->Rows[i]->Cells[j]->Value;

        }

        output->WriteLine(forOutput); // 一次寫出一列，寫完後即換行

    }

    output->Close(); // 寫完檔後務必關檔

9 9

2 2 2 2 2 2 2 2 2 

0 0 0 0 0 0 1 0 2 

2 0 1 1 1 0 1 0 2 

2 0 1 0 0 0 0 0 2 

2 0 1 1 1 1 1 1 2 

2 0 1 0 0 0 0 0 2 

2 0 1 0 1 1 1 0 2 

2 0 0 0 0 0 1 0 0 

2 2 2 2 2 2 2 2 2

--------- Read in a maze from a file as above and Show it in dataGridView ------ using stdio.h ---

private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) 

{   String ^ a; 

    int m, p, i, j; 

    char * fname;

    if (openFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK) 

    { // 順利開啟檔案才繼續往下做

        richTextBox1->LoadFile(openFileDialog1->FileName, RichTextBoxStreamType::PlainText);

        a = openFileDialog1->FileName; 

        char * str2 = (char*) (void*) Marshal::StringToHGlobalAnsi(a); 

        FILE *fp = fopen(str2,"r"); // 讀檔, 注意第二參數為 "r" (read) 

        if (fp) 

        {   fscanf(fp, "%d %d", &m, &p); 

            listBox1->Items->Add("m="+m+" p="+p); 

            listBox1->Items->Add("input file :"+a);

            // Allocate memory dynamically for **maze

            maze = new int * [m];

            for (i=0; i<m; i++) maze[i] = new int [p];

            dataGridView1->RowCount = m;  // Define the size of dataGridView1

            dataGridView1->ColumnCount = p;

            // dataGridView1->AutoSizeColumnsMode = System::Windows::Forms::DataGridViewAutoSizeColumnsMode::ColumnHeader;

            for (i=0; i<m; i++)

            {   // dataGridView1->Columns[i]->Width = 32;

                // dataGridView1->Rows[i]->Height = 32;

                for (j=0; j<p; j++)

                {   fscanf(fp, "%d", &maze[i][j]); 

                    // dataGridView1->Rows[i]->Cells[j]->Value = maze[i][j];

                }

            } 

            fclose(fp);   // close file

            for (i=0; i<m; i++)

    {   for (j=0; j<p; j++)

{   if (maze[i][j] == 2)

// dataGridView1->Rows[i]->Cells[j]->Value =  "●";

        dataGridView1->Rows[i]->Cells[j]->Style->BackColor = Color::Brown;//海軍藍;

    else 

// dataGridView1->Rows[i]->Cells[j]->Value =  maze[i][j];

        if (maze[i][j] == 1) 

    dataGridView1->Rows[i]->Cells[j]->Style->BackColor = Color::Navy;//海軍藍;

else dataGridView1->Rows[i]->Cells[j]->Style->BackColor = Color::Honeydew;//淺綠;

}  

    } 

    for (i=0; i<m; i++)    // Release memory of **maze

    { delete maze[i];

    }

    delete maze;

} 

    }

}

================================ Visual Studio 2022  =================================

// 讀檔

private: System::Void button3_Click(System::Object^ sender, System::EventArgs^ e) { 

if (openFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK) //順利開檔才要繼續做下去

{

StreamReader^ reader = gcnew StreamReader(openFileDialog1->FileName);

String^ firstLine = reader->ReadLine(); // 一次讀檔案中的一行

cli::array<String^>^ width_and_height = firstLine->Split(' ');

width = int::Parse(width_and_height[0]);

height = int::Parse(width_and_height[1]);

textBox1->Text = width_and_height[0];

textBox2->Text = width_and_height[1];

maze = new int* [height];

for (int i = 0; i < height; i++)

{

maze[i] = new int[width];

}

for (int i = 0; i < width; i++)

{

cli::array<String^>^ maze_content = reader->ReadLine()->Split(' ');

for (int j = 0; j < height; j++)

{

maze[i][j] = int::Parse(maze_content[j]);

}

}

dataGridView1->RowCount = height + 1; // 要多加 1，不然他會IndexOutOfRange，可能是dataGridView本身的設定問題

dataGridView1->ColumnCount = width;

dataGridView1->ColumnHeadersVisible = false; // 隱藏columns

dataGridView1->RowHeadersVisible = false; // 隱藏index

dataGridView1->AllowUserToAddRows = false; // 去掉最後一行空白行

//dataGridView1->AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill; // 調整欄位寬度，但不知為何這邊沒辦法用這行程式，所以手動去更改屬性的地方

for (int i = 0; i < height; i++)

{

for (int j = 0; j < width; j++)

{

dataGridView1->Rows[i]->Cells[j]->Value = maze[i][j];

}

}

draw_dataGridView();

}

}

 // 存檔

private: System::Void button4_Click(System::Object^ sender, System::EventArgs^ e) { 

// 讓系統知道存放路徑

try 

{

StreamWriter^ writer = gcnew StreamWriter(Directory::GetCurrentDirectory() + "- output.txt");

// 第一行先填入width和height

String^ firstLine = width + " " + height;

writer->WriteLine(firstLine);

// 填入迷宮內容

for (int i = 0; i < dataGridView1->RowCount; i++)

{

String^ outputString = "";

for (int j = 0; j < dataGridView1->ColumnCount; j++)

{

outputString += dataGridView1->Rows[i]->Cells[j]->Value + " ";

}

writer->WriteLine(outputString);

}

// 寫完記得關檔

writer->Close();

MessageBox::Show("Save successfully !");

}

catch(Exception^ e)

{

MessageBox::Show("Save failed !");

}

}