What exactly happens when I input a string “abcd” to scanf(“%d”, &var)?

Question

Inputting a string to

scanf("%d",&var) returns 0.

There is a similar question here , but the explanation of what happens internally is not provided. What is provided is a way to handle the situation.

How exactly does GCC handle strings passed to scanf("%d",&var) and why is the return value 0 in this case?

Answer 1

Upon successful completion, scanf shall return the number of successfully matched and assigned input items; this number can be zero in the event of an early matching failure.

On seeing %d in format string, scanf expects an int type data. When you enter string in place of int , scanf starts reading input and when sees character, stop reading and returns 0 .

Answer 2

On success, the function returns the number of items of the argument list successfully filled. So, if you don't type a number, the number of items read will be 0.

Refer to http://www.cplusplus.com/reference/cstdio/scanf/ for more info