In Eclipse: right click the project click properties Expand “C/C++ general“ the item in the left hand tree view by clicking the arrow, (just clicking the item itself does not expand the suboptions) From the suboptions select “Preprocessor Include Paths, Macros etc.“ Click the “Providers“ tab Check the box next to “CDT GCC Built-in Compiler … Read more
Is it guaranteed by the law? No. C++ says nothing about the representation of bool values. Is it guaranteed by practical reality? Yes. I mean, if you wish to find a C++ implementation that does not represent boolean false as a sequence of zeroes, I shall wish you luck. Given that false must implicitly convert … Read more
In C and C++, ZeroMemory() and memset() are the exact same thing. /* In winnt.h */ #define RtlZeroMemory(Destination,Length) memset((Destination),0,(Length)) /* In winbase.h */ #define ZeroMemory RtlZeroMemory Why use ZeroMemory() then? To make it obvious. But I prefer memset() in C or C++ programs.
I think I finally found a solution: First, in a header file, declare memset() with a pragma, like so: extern “C” void * __cdecl memset(void *, int, size_t); #pragma intrinsic(memset) That allows your code to call memset(). In most cases, the compiler will inline the intrinsic version. Second, in a separate implementation file, provide an … Read more
The simplest solution with a loop would look like this: func memsetLoop(a []int, v int) { for i := range a { a[i] = v } } There is no memset support in the standard library, but we can make use of the built-in copy() which is highly optimized. With repeated copy() We can set … Read more
Aha I checked in the glibc code and there’s a inhibit_loop_to_libcall modifier which sounds like it should do this. It is defined like this: /* Add the compiler optimization to inhibit loop transformation to library calls. This is used to avoid recursive calls in memset and memmove default implementations. */ #ifdef HAVE_CC_INHIBIT_LOOP_TO_LIBCALL # define inhibit_loop_to_libcall … Read more
In C++ std::fill or std::fill_n may be a better choice, because it is generic and therefore can operate on objects as well as PODs. However, memset operates on a raw sequence of bytes, and should therefore never be used to initialize non-PODs. Regardless, optimized implementations of std::fill may internally use specialization to call memset if … Read more
Just change to memset (arr, -1, sizeof(arr)); Note that for other values than 0 and -1 this would not work since memset sets the byte values for the block of memory that starts at the variable indicated by *ptr for the following num bytes. void * memset ( void * ptr, int value, size_t num … Read more
No, you cannot use memset() like this. The manpage says (emphasis mine): The memset() function fills the first n bytes of the memory area pointed to by s with the constant byte c. Since an int is usually 4 bytes, this won’t cut it. If you (incorrectly!!) try to do this: int arr[15]; memset(arr, 1, … Read more
Most certainly, memset will be much faster than that loop. Note how you treat one character at a time, but those functions are so optimized that set several bytes at a time, even using, when available, MMX and SSE instructions. I think the paradigmatic example of these optimizations, that go unnoticed usually, is the GNU … Read more