help me to find a bug....

[c00012]

Hello Guys,

I wrote a code to save id and password and read it using vector and structure as follows:

  #include <iostream>
  #include <fstream>
  #include <vector>
  #include <string>

  using namespace std;

  struct user
  {
	string id;
	string pwd;
  };

  vector<user> v;

  const char* filename = "test.dat";

  int main(void)
  {
	user u;//for write
	user u1;//for read

	
	ofstream ofile;
	FILE* fp = fopen(filename, "rt");

	cout << "id: ";
	cin >> u.id;
	cout << "pwd: ";
	cin >> u.pwd;

	ofile.open(filename, ios::out|ios::binary);

	if (!ofile)
	{
		cout << "failed to open!" << endl;
		return 1;
	}
	else
		cout << "saving..." << endl;
		ofile.write((char*)&u, sizeof(user));
		cout << "save complete." << endl;
	
	ofile.close();

	while (fscanf(fp, "%s %s", &u1.id, &u1.pwd)==1)
	{
		v.push_back(u1);
	}

	fclose(fp);

	cout << v.capacity() << endl;

	for (int i = 0; i < v.capacity();i++)
		cout << v[i].id << " " << v[i].pwd << endl;
	
	system("pause");
	return 0;

      }

after building this code, I've got an error message like this:
"Exception thrown at 0x00D8B410 in Prac2.exe: 0xC0000005: Access violation writing location 0xDDDDDDDD."

It seems to have a bug in this code but I can't find it out.

If you find it out, I will appreciate it very much.

thanks for your help in advance.

seihyung

[Moschops]

Pay attention to what your compiler tells you. When it warns you about things, you should read them.

while (fscanf(fp, "%s %s", &u1.id, &u1.pwd)==1)
This is an attempt to write into two char arrays. However, u1.id is not a char array and u1.pwd is not a char array.

This code is a horrible mish-mash of C and C++. Don't do that. Unless you've got a really good reason, just go with C++.

So no fopen. No FILE*. Use a C++ input file stream.

No fscanf. Use C++ input/output mechanisms.

[Chervil]

At lines 53 and 55, v.capacity() should be v.size()
reference:
http://www.cplusplus.com/reference/vector/vector/capacity/
http://www.cplusplus.com/reference/vector/vector/size/

Line 41 ofile.write((char*)&u, sizeof(user)); is not valid since user contains members of type std::string. std::string will point to data held on the heap, writing such pointers to a file will not store the actual text content.

This code is a horrible mish-mash of C and C++.

It is indeed quite a mix.

[xenoviaquarta]

what are you really coding? you are using 2 language at the same time :)

it looks like you got a segmentation fault, accessing a memory address that you dont own

i dont know fscanf() of C so i cant be much help here