Read chars from a binary file

Question

1.00/5 (1 vote)

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Hello. I'm trying to write and read from a binary file and I having some problems when I try to load the data that contains chars.

C++

 struct user {
	char *username;
	char * password;
	unsigned int ID;
 };


test_usernames_c.open("users_c.dta", ios::binary | ios::out);
user *default_user;
default_user = new user;

default_user->username = new char[7];
strcpy_s(default_user->username,7, "user11");

test_usernames_c.write((const char*)&default_user->username, 7);
//I hardcoded the size just to make sure 


test_usernames_c.close();

char *usernameX;
usernameX = new char[7];

test_usernames_c.seekg(pos_file, ios::beg);
test_usernames_c.read((char*)&usernameX, sizeof(char) * 7);

When I read the file at the end of the code I get the correct result but I get CORRUPTED STACK and Visual Studio throws an exception (Run-Time Check Failure #2 - Stack around the variable 'usernameX' was corrupted.)

Can you please tell me how to correct the code or what Im doing wrong? If I try to read the data in a user struct it works but I dont understand why since I initiate the char* in the struct and the standalone usernameX char* in the same way.

Posted 18-Dec-14 11:54am

bobos_underground

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bobos_underground 18-Dec-14 17:57pm

After I close the file I open it again with ios::in; And also seekg is irelevant;

2 solutions

Solution 2

Your buffer addressing is wrong, it should be:

C++

test_usernames_c.write(default_user->username, 7); // username is already a pointer
//I hardcoded the size just to make sure 

test_usernames_c.close();
 
char *usernameX;
usernameX = new char[7];
 
test_usernames_c.seekg(pos_file, ios::beg);
test_usernames_c.read(usernameX, sizeof(char) * 7); // usernameX is also a pointer

Posted 18-Dec-14 23:01pm

Richard MacCutchan

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BacchusBeale · Accepted Answer · 2014-12-18T12:54:00

Solution 1

Look at cplusplus website. They have:

C#

char * buffer = new char [length];

    std::cout << "Reading " << length << " characters... ";
    // read data as a block:
    is.read (buffer,length);

you don't need this:

(char*)&

does that solve your problem?

Posted 18-Dec-14 12:54pm

BacchusBeale

Comments

bobos_underground 18-Dec-14 19:01pm

Thank you.

bobos_underground 18-Dec-14 19:07pm

But its normal to write chars in the binary file so that are readable to an text editor ?