CODEWITHSUNDEEP
chexscanfformat-specifiersoctal
Chandan
Chandan

Reputation: 764

Scanning an octal and hexadecimal number in %d format specifier with scanf

  1. I was experimenting with the printing octal and hexadecimal number in C. The following is printing as expected

    int a = 012;
printf("%d",a); //printing as 10. The decimal representation of octal 12.

    However, when I am scanning 012 using %d 0 is ignored and it is printing 12. What is the reason?

    int b;
scanf("%d",&b);
printf("%d", b); //printing 12.

  2. When I am scanning 0x12 using %d the output is giving as 0 as follows

    int b;
scanf("%d",&b);
printf("%d", b); //printing 0

What is the reason for this? Why they are not giving any runtime errors?

Thanks in advance!!!

Upvotes: 0

Views: 1813

Answers (2)

ninja
ninja

Reputation: 809

Explanation

int a = 012;    // a is assigned decimal value 10 (012 is octal = 10 in decimal)
printf("%d",a); // printing a in decimal as 10

In the case of first code snippet, you are assigning a=10 (which is represented as octal 012) and printing it in decimal format.

int b;
scanf("%d",&b);  // read an integer in decimal format
printf("%d", b); //printing 12 because the input was 12 after ignoring the 0.

When you're using scanf with %d, it expects an integer in decimal format. So it ignores the first 0 and assigns b = 12. And when you print it, you see 12.

int b;
scanf("%d",&b);
printf("%d", b); //printing 0

In the above case, you are asking scanf to read an integer in decimal format and when you enter 0x12, it stops scanning at character x after reading 0 since x cannot be a part of a valid integer.

Solution

So here is the way to go.

"%d" - to input decimal value
"%o" - to input integer value in an octal format
"%x" - to input integer value in hexadecimal format
"%i" - to input integer in any format (decimal/octal/hexadecimal)

Upvotes: 1

dbush
dbush

Reputation: 225197

The %d format specifier to scanf explicitly expects a number formatted as a decimal integer. So when you enter "012" is reads 12 since the leading 0 is essentially ignored. Then when you enter "0x12", the scanning stops at the character "x" so the value 0 is read.

If you use the %i format specifier, it will use hex if the string starts with "0x", octal if it starts with "0" and decimal otherwise.

Upvotes: 2

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