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Q&A

Input taking only first character of a string

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I wrote a program named Kernel.c 2 months into my life in programming and created 4 functions at the time, and now there are 7 functions.

Recently, I updated the program completely onto an online compiler so anyone can use it not just on a university's coding sandbox (where I wrote it in the first place). I'm having trouble with inputting though.

You can take a look at the program here but the basic summary is the first input, and probably the other string inputs, where when I input something, it only results in the first character.

If I type talk, I have t. If I type feedback, I have f. I think you get the picture.

It might have to be from this portion:

char *function;
printf("What do you want me to do? ");
scanf("%s", function); // the input function
/* printf("You picked %s.\n", function)
test that shows that only the first letter is taken when given input

Question: How do I fix these inputs?

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Uninitialized pointer FAQ (1 comment)
Write the question better way (1 comment)

1 answer

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Your pointer function is uninitialized.

From some documentation pages for scanf

at https://man7.org/linux/man-pages/man3/scanf.3.html :

s
Matches a sequence of non-white-space characters; the next pointer must be a pointer to the initial element of a character array that is long enough to hold the input sequence and the terminating null byte ('\0'), which is added automatically. The input string stops at white space or at the maximum field width, whichever occurs first.

and at https://www.cplusplus.com/reference/cstdio/scanf/ :

... (additional arguments)
Depending on the format string, the function may expect a sequence of additional arguments, each containing a pointer to allocated storage where the interpretation of the extracted characters is stored with the appropriate type.

(emphasis mine)


The simplest way is probably to use a char array, and limit the field width of the %s format specifier to the size of the char array (minus the null terminator):

char function [80];
scanf("%79s", function);

(P.S.: I don't know whether the code example in your question is really the cause of the issue you experience. I have doubts, as i would rather expect the program crashing when using an uninitialized pointer like that. But hey, it's the code you have identified as being the cause of the problem, so i will go with that...)
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