Seeking a good way to teach text file modification in VC

afeng009

I store the structure in a text file (student information record name student number transcript)
For example, the content in the text file is:

MaWenTao
99001
88
LiMing
99002
92
WangFang
99003
89

Now I want to modify LingMing's information record, such as grade 92 to 95, please enlighten, I want to explain that I can not use the database, thank you!

pretty_mood

Use the string to match the structure header that needs to be modified, and then read out the modified structure content and write it to the file again.

zjwzjw

Is the file content search ~ ~

afeng009

I can do it this way, but I have to rewrite the entire file every time. I want to know if there is a method such as using the seek pointer to locate the method that can be directly modified, or there are other libraries that can directly call the method to modify it. Thank you!

afeng009

Consult the master to give the code.

zjwzjw

You can define a structure,
Three members: Name Student ID Results

Use the CFILE Read method or the standard library fread function,
Or ifsteam's read method ...

Each time you read the contents of a structure,
Then determine whether the name is a record that needs to be modified,
If yes, modify it,
If not, continue to read the information of the next record.

After modification, just write the record back to the file,
Pay attention to adjust the position of the file pointer ~~

superandy

If the modification is not of equal length, you can only rewrite the entire file at a time

afeng009

Should be modified

lzy105

You try
#include <iostream>
#include <string>
#include <fstream>
using namespace std;

typedef struct {
long long ID;
string name;
int r1, r2, r3;
} data, * pdata;
  
  int main ()
  {
data d;
d.ID = 5050379001;
d.name = "4k.grubby";
d.r1 = 85;
d.r2 = 87;
d.r3 = 83;
data d0, d1;
d0.ID = 5050379002;
d0.name = "john";
d0.r1 = d0.r2 = d0.r3 = 90;
d1.ID = 5050379003;
d1.name = "tom";
d1.r1 = d1.r2 = d1.r3 = 87;
  ofstream File ("student.db", ios :: binary); // New binary file
  File.write ((const char *) (&d), sizeof (data));
  File.write ((const char *) (&d0), sizeof (data));
  File.write ((const char *) (&d1), sizeof (data));
  d1.name = "jerry"; // Modify the data
  File.seekp (2 * sizeof (data)); // Move to the third group of data
  File.write ((const char *) (&d1), sizeof (data)); // Overwrite
  File.close ();
  ifstream iFile ("student.db", ios :: binary);
  data d2;
  iFile.seekg (sizeof (data) * 2);
  iFile.read ((char *) (&d2), sizeof (data));
  cout << d2.name << d2.ID << endl;
  iFile.close ();
  }