从二进制文件中读取字符 [英] Read chars from a binary file

问题描述

您好。我正在尝试编写和读取二进制文件，当我尝试加载包含字符的数据时遇到一些问题。

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.

 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);

当我在代码末尾读取文件时，我得到了正确的结果但是我得到了CORRUPTED STACK并且Visual Studio抛出异常（运行时检查失败＃2 - 变量'usernameX'周围的堆栈已损坏。）



你能告诉我如何更正代码或我做错了什么？如果我尝试读取用户结构中的数据它可以工作，但我不明白为什么，因为我以相同的方式在结构中启动char *和独立的usernameX char *。

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.

推荐答案

看看cplusplus网站。它们有：

Look at cplusplus website. They have:

char * buffer = new char [length];

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

你不需要这个：

you don't need this:

(char*)&

可以解决您的问题吗？

does that solve your problem?

您的缓冲区寻址是错误的，它应该是：

Your buffer addressing is wrong, it should be:

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

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