What Does (~0L) Mean?
I'm Doing Some X11 Ctypes Coding, I Don't Know C but Need Some Help Understanding This. in the C Code Below (Might Be C++ Im Not Sure) We See (~0L) What Does...
I'm doing some X11 ctypes coding, I don't know C but need some help understanding this.
In the C code below (might be C++ im not sure) we see (~0L) what does that mean? In Javascript and Python ~0 means -1.
812 int result = GetProperty(window, property_name,
813 (~0L), // (all of them)
814 &type, &format, &num_items, &properties);
Thanks
2 Answers
0L is a long integer value with all the bits set to zero - that's generally the definition of 0. The ~ means to invert all the bits, which leaves you with a long integer with all the bits set to one.
In two's complement arithmetic (which is almost universal) a signed value with all bits set to one is -1.
The reason for using ~0L instead of -1L is to be clearer about the intent - it's not meant to be used as a number at all, but rather as a collection of bits.
Bitwise compliment of zero of long type.
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