How to copy a string into a char array in C++ without going over the buffer

Question

I want to copy a string into a char array, and not overrun the buffer.

So if I have a char array of size 5, then I want to copy a maximum of 5 bytes from a string in

Answer 1

std::string str = "Your string";
char buffer[5];
strncpy(buffer, str.c_str(), sizeof(buffer)); 
buffer[sizeof(buffer)-1] = '\0';

The last line is required because strncpy isn't guaranteed to NUL terminate the string (there has been a discussion about the motivation yesterday).

If you used wide strings, instead of sizeof(buffer) you'd use sizeof(buffer)/sizeof(*buffer), or, even better, a macro like

#define ARRSIZE(arr)    (sizeof(arr)/sizeof(*(arr)))
/* ... */
buffer[ARRSIZE(buffer)-1]='\0';