How to memset an array of bools?

c memset array to zero
memset 2d array
memset vector
memset in java
memset char array
memset in cpp for array
initialize bool array c++
memset array c
void *memset(void *dest, int c, size_t count)

The 3rd argument is the Number of characters or bytes in the array. How would you memset an array of booleans, say bool bArray[11]?

MSDN says: "Security Note - Make sure that the destination buffer has enough room for at least count characters."

std::fill() should use memset() when possible.

std::fill(std::begin(bArray), std::end(bArray), value);

Using memset on array of bool (C++), If the object is not trivially-copyable (e.g., scalar, array, or a C-compatible void* memset( void* str, int ch, size_t n); Parameters str[] : Pointer to the object to  memset() is used to fill a block of memory with a particular value. The syntax of memset() function is as follows : // ptr ==> Starting address of memory to be filled // x ==> Value to be filled // n ==> Number of bytes to be filled starting // from ptr to be filled void *memset(void *ptr, int x, size_t n);

memset(buffer_start, value, sizeof(bool) * number_of_bools);

memset in C++, What is a fast way to initialize a bool array ? A. For true or false you can use memset(). Often the compiler can turn that into a single machine  To use memset, find the starting address of the array (that's easy - it's the value of the array variable, or the address of the element with all indices = 0, if you prefer to be more explicit). Then find the length of the array; this can be trickier. Once both are known, call memset.

To set array of 11 bool elements to e.g. true by using memset:

const int N = 11;
bool arr[N];
memset(&arr, 1, sizeof(bool) * N);

What is a fast way to initialize a bool array ?, BOOL bMyarray[1000]; memset(bMyArray , 0xFF, sizeof(BOOL) * 1000); clean & quick until someone else's code found I was returning -1 to The memset() function fills the first n bytes of the memory area pointed to by s with the constant byte c. It is obvious that memset can't be used to initialize int array as shown below: int a[10]; memset(a, 1, sizeof(a));

//Array declaration
bool arr[10];

//To initialize all the elements to true

memset(arr,1,sizeof(arr));

Similarly, you can initialize all the elements to false, by replacing 1 with 0.

Initialising a BOOL array to TRUE ?? - C / C++, Originally Answered: Whether I should use vector<bool> or regular arrays for implementing Sieve of Eratosthenes? A standard C++ vector has only two  memset sets memory in multiples of bytes. So, the only way is to add padding to your bool pointer such that its length is a multiple of 8. Then do memset. Personally I would prefer if there were any other alternative than putting a redundant padding. But I haven't found any alternative solution to date.

memset sets memory in multiples of bytes. So, the only way is to add padding to your bool pointer such that its length is a multiple of 8. Then do memset. Personally I would prefer if there were any other alternative than putting a redundant padding. But I haven't found any alternative solution to date.

Should I use a vector<bool> or a regular array for implementing , If i DO then how do I set all values of a 2 dimensional boolean array to true. Last edited on Apr 9, I especially wouldn't use memset on bools. This is in no way like memset. It returns a new byte array rather than changing the contents of an existing byte array, which is a huge difference in many applications of memset. – Matt Jun 6 '14 at 6:04. Actually, there is little known IL operation called Initblk ( English version) which does exactly that. So, let's use it as a method that

Do booleans start off true or false? - C++ Forum, memset doesn't care how you allocate memory. You can call memset on any value that has a memory address (e.g. ints, bools, bool arrays, int  memset in C++ Converts the value ch to unsigned char and copies it into each of the first n characters of the object pointed to by str[]. If the object is not trivially-copyable (e.g., scalar, array, or a C-compatible struct), the behavior is undefined.

Initialize Array of Boolean Values, Memset() is the most inefficient and dangerous function. This error occurred because in C and C++ you cannot pass arrays by value. bool TryStrongCasting​( pDynamicCastFunction pCandidateFunction) const; virtual bool  std::memset(buffer, 0, sizeof(*buffer) * ARRAY_LENGTH); This code remains correct if the type of buffer changes, provided of course that it continues to have ARRAY_LENGTH elements of whatever type that is, and provided that all-bits-zero remains the correct initial value.

The most dangerous function in the C/C++ world, efficient arrays of booleans -- C extension. C-function by using memset; fix issue #74, bitarray is hashable on Python 2; fix issue #68, unittest. The memset() function fills the first n bytes of the memory area pointed to by s with the constant byte c. It is obvious that memset can’t be used to initialize int array as shown below: int a[10]; memset(a, 1, sizeof(a)); it is because int is represented by 4 bytes (say) and one can not get the desired value for the integers in array a.

Comments
  • bool bArray[11] = {}? Or std::fill(begin(bArray), end(bArray), true)?
  • 11 * sizeof(bool). That being said, that's not very c++; you should be using std::fill()
  • Seems vector<bool> is optimized for space allocation and is a 'real' array of bits. A C++ style array of bools is essentially an array of bytes with all bits either 0 or 1. Vector<bool> is the way to go. Thanks for all the responses. Much appreciated.
  • @user173438: vector<bool> is slow. You probably wanted std::bitset.
  • @user173438: vector<bool> is also (surprisingly) not a normal container, unlike vector. See explanation here: books.google.de/…
  • If he gets bArray via a pointer, how can you get std::end(bArray)?
  • @einpoklum If bArray is a pointer, this line should be std::fill(bArray, bArray + arraySize, value);
  • @MewX: Obviously, but that's not what this answer says right now.
  • sizeof(bool) makes little sense there - memset just fills each byte with a bool.
  • @blaisorblade Yes sizeof(bool) == 1, but clearly stating your intent in code is never a bad thing.
  • Size of bool may not be 1.
  • Elaborating on what Neil said, as per 5.3.3/1: "sizeof(char), sizeof(signed char) and sizeof(unsigned char) are 1. The result of sizeof applied to any other fundamental type (3.9.1) is implementation-defined. [ Note: in particular, sizeof(bool), sizeof(char16_t), sizeof(char32_t), and sizeof(wchar_t) are implementation-defined."
  • It should be memset(arr, 1, sizeof(bool) * N);