9+ Fopen_s 使い方 Ideas

[ C++ ] error C4996 'fopen' This function or variable may be unsafe from cibochan.blogspot.com

Introduction

Fopen_s is a function used in the C programming language to open a file. It is a secure version of the fopen function that helps prevent buffer overflow vulnerabilities. This article will provide you with a complete guide on how to use the fopen_s function.

Why Use Fopen_s?

Fopen_s is a more secure version of the fopen function. It takes three arguments: the file pointer, the filename, and the mode. The file pointer is a pointer to the file to be opened, the filename is the name of the file to be opened, and the mode is the type of access to the file.

What Are the Different Modes?

There are several modes that can be used when opening a file using fopen_s:

"r" – Read mode
"w" – Write mode
"a" – Append mode
"r+" – Read and write mode
"w+" – Write and read mode
"a+" – Append and read mode

How to Use Fopen_s?

To use the fopen_s function, you need to include the stdio.h header file. The syntax for the fopen_s function is as follows:

errno_t fopen_s(FILE** pFile, const char* filename, const char* mode);

The function returns an error code that indicates whether the file was opened successfully. The error codes are defined in the errno.h header file.

Example Code

Here is an example of how to use the fopen_s function in C:

#include  #include  int main() { FILE* file; errno_t err; err = fopen_s(&file, "example.txt", "w"); if (err != 0) { printf("File could not be opened. Error code: %d\n", err); } else { printf("File opened successfully.\n"); fclose(file); } return 0; }

In this example, we are opening a file named "example.txt" in write mode. If the file cannot be opened, the program will display an error message. If the file is opened successfully, the program will display a success message and then close the file.

Conclusion

In conclusion, the fopen_s function is a secure version of the fopen function that helps prevent buffer overflow vulnerabilities. It is a useful function to use when opening files in C programming. By following the guide provided in this article, you should now have a better understanding of how to use the fopen_s function in your programs.