strncpy problem

why can't I do :

strncpy (str2,NULL,5);

Why? Because NULL is not a string.
Where is strncpy supposed to read the data (the source) to copy into the destination?

so what do I do to assign str2 to NULL?

If str2 is an array:

Code:

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str2[0] = '\0';

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If str2 is a pointer:

Code:

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str2 = NULL;

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or if the string contains something sensitive like passwords, and you want to be extra secure, you can wipe the whole string like this:

Code:

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memset( str2, '\0', sizeof( str2 ) );

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Of course sizeof will only work if str2 is an array; if it's a pointer you need to know the actual size...

In most cases though, I'd just set the first character to NUL like Elysia showed.