奇怪的 output 编号（C）

Question

#include<stdio.h>

int main(void)

{

    int h;
    int m;
    scanf_s("%d : %d", &h,&m);
    printf("%d : %d", h,m);

    return 0;
}

That is it, I typed 12 13 It gave me 12: -858993460

ironic.. would you give me an idea?

Answer 1

If you typed exactly "12 13" as you wrote in the question, then the issue is that your input does not match the format specified in your call to scanf . In particular, scanf is only looking for input in the form of <some integer>: <some integer> . Note that your input does NOT include the : character. As such, scanf only successfully reads a number into your first variable ( h ), but fails to read into the second variable ( m ).

You can confirm this is the case by checking the return value of scanf , which returns "the number of input items successfully matched" (see the man page ).

The reason you're seeing a "random" number in the output is that your variable m is never initialized. If you instead initialize it to 0 , then you will no longer see a "random" value. This is good practice anyway.

For example (with error check):

#include<stdio.h>

int main(void)

{

    int h = 0;
    int m = 0;
    int rc = scanf_s("%d : %d", &h,&m);
    if (rc != 2) { // expect to read 2 values
        printf("scanf failed, read %d value(s)\n", rc);
    } else {
        printf("%d : %d", h,m);
    }

    return 0;
}

Answer 2

Keep the format in scanf_s("%d: %d", &h,&m);

scanf() : The C library function int scanf(const char *format, ...) reads formatted input from stdin.

In your case, type 12: 13

Answer 3

Your call to the scanf_s function expects a colon in the input, but you didn't type one, so nothing got stored in m in the call. As a result, you got a garbage value for m (as you didn't initialize it either). If you type in 12: 13 , then you should get the expected result.

Also, make sure to check the return value of scanf_s to make sure that you've got all of the values you want.