Why should one use strncpy() and not strcpy()? What are the problems with strncpy()?

strcpy() is the cause of many bugs. Thats because programmers almost always end up copying more data into a buffer than it can hold. To prevent this problem, strncpy() comes in handy as you can specify the exact number of bytes to be copied.

But there are problems with strncpy() also. strncpy() does not always place a '\0' terminator in the destination string. (Funnily, it pads short strings with multiple \0's, out to the specified length). We must often append a '\0' to the destination string by hand. You can get around the problem by using strncat() instead of strncpy(): if the destination string starts out empty, strncat() does what you probably wanted strncpy() to do. Another possibility is sprintf(dest, "%.*s", n, source). When arbitrary bytes (as opposed to strings) are being copied, memcpy() is usually a more appropriate function to use than strncpy().