Getch c ошибка

Once upon a time, if you called a function which the compiler had never heard of, like this:

#include <stdio.h>
int main()
{
    int x = foo();
    printf("%dn", foo);
}

Anyway, if you did that, the compiler quietly assumed that foo() was a function returning int. That is, the compiler behaved just as if you had typed

extern int foo();

somewhere before you called foo.

But in, I think, C99, the language was changed. It was no longer legal to call a function you had not explicitly declared. Because there was lots and lots of code out there that was written under the previous set of rules, most compilers did not immediately begin rejecting the old-style code. Some continued to quietly assume that unrecognized functions returned int. Others — like yours — began noisily assuming that unrecognized functions returned int, emitting warnings along the lines of «‘foo’ undefined, assuming extern returning int».

It sounds like your question is that some time ago, your code containing calls to getch() was accepted without warning, but today, you’re getting the warning «‘getch’ undefined, assuming extern returning int». What changed?

One possibility is that your code changed slightly. If your code used to contain the line

#include <conio.h>

somewhere, that file would have contained a declaration along the lines of

extern int getch();

and this would have goven the compiler the declaration that it needed, and you would not have gotten the warning. But if today your code does not contain that #include line, that explain why the warning started cropping up.

It’s also possible that your compiler has changed somehow. It’s possible you’re using a new version of the compiler, that’s more fussy, that has gone from quietly assuming, to normally assuming. Or, it’s possible that your compiler options have changed. Many compilers can be configured to accept different variants of the language, corresponding to the different versions of the language standards that have been released over the years. For example, if some time ago your compiler was compiling for language standard «C89», but today, it’s doing «C99» or «C11», that would explain why it’s now being noisy with this warning.

The change in the compiler could be a change in the defaults as configured by a system administrator, or a change in the way you’re invoking the compiler, or a change in your project’s Makefile, or a change in the language settings in your IDE, or something like that.

A few more points:

• getch is not a Standard C function; it’s specific to Windows. Your program would be more portable, in general, if you didn’t use it. Are you sure you need it? (I know what it’s for; what I don’t know if there’s some other way of keeping your program’s output window on the screen after if exits.)
• You should get in the habit of declaring main() as int, not void. (void will work well enough, but it’s not correct, and if nothing else, you’ll get lots of negative comments about it.)
• I think there’s something wrong with your call to strcpy_S, too,

Once upon a time, if you called a function which the compiler had never heard of, like this:

#include <stdio.h>
int main()
{
    int x = foo();
    printf("%dn", foo);
}

Anyway, if you did that, the compiler quietly assumed that foo() was a function returning int. That is, the compiler behaved just as if you had typed

extern int foo();

somewhere before you called foo.

But in, I think, C99, the language was changed. It was no longer legal to call a function you had not explicitly declared. Because there was lots and lots of code out there that was written under the previous set of rules, most compilers did not immediately begin rejecting the old-style code. Some continued to quietly assume that unrecognized functions returned int. Others — like yours — began noisily assuming that unrecognized functions returned int, emitting warnings along the lines of «‘foo’ undefined, assuming extern returning int».

It sounds like your question is that some time ago, your code containing calls to getch() was accepted without warning, but today, you’re getting the warning «‘getch’ undefined, assuming extern returning int». What changed?

One possibility is that your code changed slightly. If your code used to contain the line

#include <conio.h>

somewhere, that file would have contained a declaration along the lines of

extern int getch();

and this would have goven the compiler the declaration that it needed, and you would not have gotten the warning. But if today your code does not contain that #include line, that explain why the warning started cropping up.

It’s also possible that your compiler has changed somehow. It’s possible you’re using a new version of the compiler, that’s more fussy, that has gone from quietly assuming, to normally assuming. Or, it’s possible that your compiler options have changed. Many compilers can be configured to accept different variants of the language, corresponding to the different versions of the language standards that have been released over the years. For example, if some time ago your compiler was compiling for language standard «C89», but today, it’s doing «C99» or «C11», that would explain why it’s now being noisy with this warning.

The change in the compiler could be a change in the defaults as configured by a system administrator, or a change in the way you’re invoking the compiler, or a change in your project’s Makefile, or a change in the language settings in your IDE, or something like that.

A few more points:

• getch is not a Standard C function; it’s specific to Windows. Your program would be more portable, in general, if you didn’t use it. Are you sure you need it? (I know what it’s for; what I don’t know if there’s some other way of keeping your program’s output window on the screen after if exits.)
• You should get in the habit of declaring main() as int, not void. (void will work well enough, but it’s not correct, and if nothing else, you’ll get lots of negative comments about it.)
• I think there’s something wrong with your call to strcpy_S, too,