C ++写入文件

Question

I have a program which writes to text file.

Example in my textfile:

4
QA131 100 100 100 100
QA132 100 100 100 100
QA133 100 100 100 100
QA134 100 100 100 100

I want to write a new line which store the record and the 4 will turn into 5.

What is the method used to write to the file?

Here is my code:

void inputRecord()
{
    Product product[101];
    char FILENAME[20];

  cout<<"Enter the file you want to open: ";
  cin>>FILENAME;
  ifstream read(FILENAME);
  if (read.is_open())
  {
      while(read.good())
      {
          read>>product[0].line;
            for(int i =0;i< product[0].line;i++)
            {
                read >>product[i].PartNumber 
                     >>product[i].initialQuantity
                     >>product[i].quantitySold 
                     >>product[i].minQuantity
                     >>product[i].price;
            }
             product[0].line+=1;
      }
      read.close();
  }




    ofstream write(FILENAME);
    write<<product[0].line << endl;
             for(int i =0;i< product[0].line;i++)
                {
                    write << product[i].PartNumber << '\t'
                          << product[i].initialQuantity << '\t'
                          << product[i].quantitySold << '\t'
                          << product[i].minQuantity << '\t'
                          << product[i].price << '\t' << endl;
                }
    write.close();

    cout << "Inventory added successfully!" << endl;
    system("pause");
    system("CLS");

}

I cannot write the item to the file.

Answer 1

you could just use fseek to solve your problem.

Here's a really simple example based this C++ reference example

#include<cstdio>

int main(void) {
  FILE * pFile;
  pFile = fopen ( "test.txt" , "wb" );

  fprintf(pFile,"00000\n"); // watch spacing

  for (int i=1; i<11; i++) {
    fprintf (pFile, "%d. This line a line of stuff.\n",i);
  }

  fseek(pFile , 0 , SEEK_SET );
  fprintf(pFile,"10   \n"); 
  fclose(pFile);

  return 0;
}