Access Violation Error when reading a string in C

Question

According to the book: How to C Programming - Eighth Edition (by Deitel brothers) this code reads the word "Hello":

#define SIZE 20

int main()
{
   char MyStr[SIZE];

   printf("Enter your word: ");
   scanf("%19s", MyStr);
}

This picture is from the Sixth Edition online:

But when I do:

int main()
{
   char MyStr[20];

   printf("Enter your word: ");
   scanf_s("%19s", MyStr);
}

I get Access Violation error:

What is that I am doing wrong?

I recommend that you read the documentation for scanf_s. It's a special function that requires special extra arguments in some cases. — Some programmer dude
– Some programmer dude, Commented Nov 1, 2018 at 12:35
"scanf_s requires the buffer size to be specified for all input parameters of type c, C, s, S, or [. The buffer size is passed as an additional parameter immediately following the pointer to the buffer or variable." — Paul Ogilvie
– Paul Ogilvie, Commented Nov 1, 2018 at 12:45
You've fallen into the trap of Microsoft telling you to use scanf_s and lies about scanf not being "safe" and whatnot - there is no change in safety here between scanf and scanf_s given the format from the book. — Antti Haapala
– Antti Haapala, Commented Nov 1, 2018 at 12:46
@Someprogrammerdude That's not the documentation for scanf_s. It is found in Annex K of the standard, the "bounds checking interface". — Lundin
– Lundin, Commented Nov 1, 2018 at 12:50
@Lundin Unfortunately Visual Studio have their own variants of the "safe" functions, that are similar but not the same as the standard functions of the same name (at least they used to be a little different). — Some programmer dude
– Some programmer dude, Commented Nov 1, 2018 at 12:51

Sandra K · Accepted Answer · 2018-11-01 13:43:50Z

3

There is a difference between scanf and scanf_s. The latter requires the length to be specified. So your code should be changed to:

int main()
{
   char MyStr[20];

   printf("Enter your word: ");
   scanf_s("%19s", MyStr, sizeof(MyStr));
}

or

int main()
{
    char MyStr[20];

    printf("Enter your word: ");
    scanf("%19s", MyStr);
}

edited Nov 1, 2018 at 13:43

Sandra K

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answered Nov 1, 2018 at 12:43

JonBelanger

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3 Comments

Sandra K Over a year ago

My IDE is not allowing me to use scaf(), so I added the size parameter to scanf_s() and it worked.

Sandra K Over a year ago

@Lundin Yeah and make the solution even more complex by finding a better book

Lundin Over a year ago

@SandraK Learning bad, non-standard practices with an outdated compiler isn't going to make you a decent C programmer. Visual Studio is at best to be regarded as a C++ compiler.

Rez Trentnor · Accepted Answer · 2018-11-01 13:57:32Z

0

Add _CRT_SECURE_NO_WARNINGS to linker options and it should allow you to use scanf and other "unsecure" methods if you don't want to use safe ones. Visual Studio by default prefers if you use secure ones

answered Nov 1, 2018 at 13:57

Rez Trentnor

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