问题
char x [1000];
x = 'hello';
What would I use to clear the contents of x? I'm not able to re-initialise it, use strcpy(x, '/0') or free().
回答1:
You cannot assign anything to an array, which your variable x is. So therefore anything that starts with x = is wrong. Secondly 'hello' is not a string, it is a multicharacter literal which is of type int, so this doesn’t make sense either. A string literal is enclosed by " while character (or multicharacter) literals are enclosed by '.
So if you want to fill your buffer x with the string "hello" you use strncpy or even better strlcpy if available:
strncpy( x, "hello", sizeof( x ) );
strlcpy( x, "hello", sizeof( x ) );
The strlcpy function is better because it always terminates the string with a nul character.
If you want to clear it you could do what the other answers suggested. I’d suggest using strncpy or strlcpy with an empty string as @codaddict suggested. That is the code that says most obviously "hey, I want to clear that string". If you want to remove the whole contents of the string from memory (for example if it contained a password or something like this) use memset as @Ken and @Tom suggested.
Also note that you never ever use functions like strcpy or strcat that don’t accept the size of the output buffer as a parameter. These are really not secure and cause nasty bugs and security vulnerabilities. Don’t even use them if you know that nothing can go wrong, just make a habit of using the secure functions.
回答2:
Usage of free() would be wrong, since x is in the stack.
What do you mean by clear? Set it to a default value? Can you use memset? (I'm copying your code as it is)
#define CLEAR(x) memset(x,'\0',1000)
char x[1000];
x= 'hello';
CLEAR(x)
If not, you can always use a for loop.
回答3:
x='hello';
may not be doing what you expect because ' denotes a character constant (or in this case a multi-character constant) not a string.
In fact, gcc won't accept the above code, complaining that 'hello' is to long (that's on a machine with 4 byte ints), and that x = 'hell' is an incompatible assignment because a char[] is not the same as an int.
Nor should
char x[1000];
x="hello";
work because you can't assign arrays that way.
回答4:
If by "clear" you mean "clear all bits in the array", how about memset(x, '\0', 1000);?
回答5:
To clear it, you would just reset it all to zero with memset().
char x[1000];
//...
memset(x, 0, sizeof (x));
来源：https://stackoverflow.com/questions/3831191/how-do-i-clear-an-array-in-c