How to Fix C4996 “This function or variable may be unsafe” in Visual Studio

Short answer: Visual Studio flags older C functions such as scanf, strcpy and fopen. Many of them can write past the end of an array if they’re used carelessly. C4996 is a warning, but with SDL checks on, it becomes an error and your program won’t build. In C++, the best fix is to use std::cin, std::string and std::ifstream instead. To keep the C function, use the _s version it suggests, or put #define _CRT_SECURE_NO_WARNINGS above all your #include lines.

What the Message Says

Here’s the full message from a Visual Studio build:

error C4996: 'scanf': This function or variable may be unsafe. Consider using scanf_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.

It names the function, suggests a replacement (scanf_s), and tells you how to switch the message off.

Microsoft’s documentation explains that most of the flagged functions can read or write a buffer without checking its size, so a careless call can run past the end of an array. That’s why safer _s versions exist. The message comes from Microsoft’s libraries, not from the C++ standard. GCC and Clang compile the same code without a word.

Why It’s an Error, Not a Warning

C4996 is officially a level 3 warning. You get error C4996 instead when your project has SDL checks turned on, which compiles with /sdl. Microsoft’s documentation lists C4996 among the warnings /sdl turns into errors.

To see the setting: Project > Properties > Configuration Properties > C/C++ > General > SDL checks.

Turning SDL checks off only turns the error back into a warning, and /sdl adds other safety checks you’d lose too. Fixing the code is the better choice.

Fix 1: Use the C++ Way (Best)

For the functions beginners meet most often, C++ has a replacement that Visual Studio doesn’t flag.

scanf → std::cin

#include <cstdio>

int main() {
    int age;
    scanf("%d", &age);
    printf("You are %d\n", age);
}

MSVC:   error C4996: 'scanf': This function or variable may be unsafe. Consider using scanf_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.

#include <iostream>

int main() {
    int age;
    std::cin >> age;
    std::cout << "You are " << age << '\n';
}

strcpy → std::string

#include <cstring>
#include <iostream>

int main() {
    char name[20];
    strcpy(name, "Sam");
    std::cout << name << '\n';
}

MSVC:   error C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.

name has room for 19 characters plus the '\0' that ends the text. strcpy doesn’t check that. Copy in a longer name and it writes past the end of the array, into whatever memory comes next. That’s the danger the warning is about. A std::string grows to fit:

#include <iostream>
#include <string>

int main() {
    std::string name = "Sam";
    std::cout << name << '\n';
}

See string vs char array for the full comparison.

fopen → std::ifstream

#include <cstdio>

int main() {
    FILE* file = fopen("scores.txt", "r");
    if (file) {
        fclose(file);
    }
}

MSVC:   error C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.

#include <fstream>
#include <iostream>

int main() {
    std::ifstream file("scores.txt");
    if (!file) {
        std::cout << "Could not open scores.txt\n";
    }
}

More in file handling in C++.

Fix 2: Use the _s Version

If you’re writing C-style code on purpose, use the function the message suggests. The _s versions take extra information, usually the size of your buffer, so they can stop before running past the end:

#include <cstring>
#include <iostream>

int main() {
    char name[20];
    strcpy_s(name, sizeof(name), "Sam");
    std::cout << name << '\n';
}

For numbers, scanf_s("%d", &age); works exactly like scanf. For text, it’s different: with %s, %c or %[, Microsoft’s documentation says you must pass the buffer size as an extra argument straight after the buffer, for example scanf_s("%19s", name, (unsigned)sizeof(name));.

The catch is that these functions come from Microsoft’s runtime. GCC and Clang on Linux don’t provide them, so this code won’t build there: GCC says 'strcpy_s' was not declared in this scope. If your code needs to build on other systems as well, prefer Fix 1.

Fix 3: Turn the Warning Off

If you understand the risk and want to keep the original functions, for example to follow a C course or book, you can switch C4996 off.

Define _CRT_SECURE_NO_WARNINGS before every #include:

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>

int main() {
    int age;
    scanf("%d", &age);
}

It has to come first. This version still gives C4996:

#include <cstdio>
#define _CRT_SECURE_NO_WARNINGS

int main() {
    int age;
    scanf("%d", &age);
}

The header checks for the macro when it’s included, so a #define after the #include comes too late.

Or set it for the whole project: Project > Properties > Configuration Properties > C/C++ > Preprocessor > Preprocessor Definitions, and add _CRT_SECURE_NO_WARNINGS. Use this if your .cpp files begin with #include "pch.h", or if you have several files to fix.

Or disable warning 4996 itself: add #pragma warning(disable : 4996) at the top of the file, or add 4996 under C/C++ > Advanced > Disable Specific Warnings. This hides every C4996, including ones about other deprecated features you might want to see, so the macro is the more targeted option.

The POSIX Version: getch and Friends

A second kind of C4996 has a different message:

#include <conio.h>
#include <iostream>

int main() {
    std::cout << "Press any key to exit...";
    getch();
}

MSVC:   error C4996: 'getch': The POSIX name for this item is deprecated. Instead, use the ISO C and C++ conformant name: _getch. See online help for details.

This time only the name is deprecated, not the function. Fix: add the underscore and call _getch(). _CRT_SECURE_NO_WARNINGS doesn’t silence this version; the macro for POSIX names is _CRT_NONSTDC_NO_WARNINGS.

<conio.h> is Windows-only. MinGW’s GCC accepts getch() without complaint, but on Linux, GCC stops with fatal error: conio.h: No such file or directory.

Common C4996 Functions

The suggested replacements are the ones Visual Studio’s messages name. For splitting text without strtok, see how to split a string.

Quick Reference

For other common messages, see C++ error messages explained.

Take Your C++ Further

Memory bugs make much more sense once you can picture the stack and the heap. C++ Better Explained walks through how C++ manages memory, from new and delete to smart pointers, with diagrams and plain-English analogies.

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Related Articles

• C++ Error Messages Explained — the most common errors and what they mean.
• C++ string vs char Array — why std::string avoids buffer overruns.
• File Handling in C++ — reading and writing files with streams.
• Getting User Input with cin — the C++ replacement for scanf.
• How to Split a String in C++ — without strtok.