how to load a char[] that's a member of Stuct[i]? - c

Question

Let's say we have this struct
struct Foo{
int FooLength; //length of Foo
char FooChar[4];
};
and then in the main we have
int sizeFoo = 100; struct Foo myFooList[sizeFoo];
what would be the best way to input data for FooChar? Would strncpy, or memcpy, or snprintf, or sprintf?
what I wish to do is something like
myFooList[0].FooLength = 3;
myFooList[0].FooChar = "dog";
myFooList[1].FooLength = 3;
myFooList[1].FooChar = "cat";
.
.
.
with a correct syntax since in C you can't just = "string"; here, and I'm not sure what would be the best way to go about it? I have look at similar topics, but I just get more confused with how strncpy or sprintf are not good or you have to have a \0 added at the end or some other detail that makes picking what to do more difficult.
Also if all the values of myFooList[] are already know (they are const or static) is there a way to initialize like one would do any other array?

Answer 1

If your input is always 3 characters, you can use strcpy, otherwise use strncpy(myFooList[0].FooChar, "dog", 3). You must add the terminating null character if using strncpy. strcpy will add the termination null character automatically, just like VHS has in his answer. In either case, you should still validate that your input does not exceed the maximum length. To find the length of a string(i.e. the number of char characters up to the first null character), you would use strlen. To determine the capacity of a char a[], you can use _countof(a). Don't forget that one of those has to be a '\0'.
memcpy would also work, but it would be unusual to do that with a string.
You wouldn't use sprintf here. sprintf would normally be used when you need to create a unique string using dynamic data at runtime. This is not what you're doing here. If you have any experience with .NET, it is the C equivalent of string.Format.
To initialize an array of 'Foo', you will just need to write a function that will do that. Even if you figure out the syntax to do it in one line, it'll be very difficult to read and maintain. Here's an example without validation, I will leave that task to you.
myFooList[0].FooLength = 3;
strncpy(myFooList[0].FooChar, "dog", 3);
myFooList[0].FooChar[3] = '\0';
myFooList[1].FooLength = 3;
strncpy(myFooList[1].FooChar, "cat", 3);
myFooList[1].FooChar[3] = '\0';

Answer 2

Your integer assignment is correct, but the string assignment is not. Following is the right way:
myFooList[0].FooLength = 3;
strcpy( myFooList[0].FooChar, "dog");
myFooList[1].FooLength = 3;
strcpy(myFooList[1].FooChar, "cat");

Answer 3

what would be the best way to input data for FooChar? Would strncpy,
or memcpy, or snprintf, or sprintf? ...
but I just get more confused with how strncpy or sprintf are not good
or you have to have a \0 added at the end or some other detail that
makes picking what to do more difficult.
Well, memcpy is a good choice if you don't want terminate nul byte. I don't really understand what is your question here.
Also if all the values of myFooList[] are already know (they are const
or static) is there a way to initialize like one would do any other
array?
In your example, no, because you use VLA who can't be initialize. But you could do the following:
#include <stdio.h>
struct Foo {
int FooLength; // length of Foo
char FooChar[4];
};
int main(void) {
struct Foo myFooList[] = {{3, "dog"}, {3, "cat"}};
size_t size = sizeof myFooList / sizeof *myFooList;
}