C++ 数组初始化

Question

is this form of intializing an array to all 0s

char myarray[ARRAY_SIZE] = {0} supported by all compilers? ,

if so, is there similar syntax to other types? for example

bool myBoolArray[ARRAY_SIZE] = {false} 

Answer 1

Yes, this form of initialization is supported by all C++ compilers. It is a part of C++ language. In fact, it is an idiom that came to C++ from C language. In C language = { 0 } is an idiomatic universal zero-initializer . This is also almost the case in C++.

Since this initalizer is universal, for bool array you don't really need a different "syntax". 0 works as an initializer for bool type as well, so

bool myBoolArray[ARRAY_SIZE] = { 0 };

is guaranteed to initialize the entire array with false . As well as

char* myPtrArray[ARRAY_SIZE] = { 0 };

in guaranteed to initialize the whole array with null-pointers of type char * .

If you believe it improves readability, you can certainly use

bool myBoolArray[ARRAY_SIZE] = { false };
char* myPtrArray[ARRAY_SIZE] = { nullptr };

but the point is that = { 0 } variant gives you exactly the same result.

However, in C++ = { 0 } might not work for all types, like enum types, for example, which cannot be initialized with integral 0 . But C++ supports the shorter form

T myArray[ARRAY_SIZE] = {};

ie just an empty pair of {} . This will default-initialize an array of any type (assuming the elements allow default initialization), which means that for basic (scalar) types the entire array will be properly zero-initialized.

Answer 2

请注意，'='在C ++ 11通用初始化语法中是可选的，并且它通常被认为是更好的写入样式：

char myarray[ARRAY_SIZE] {0}

Answer 3

Yes, I believe it should work and it can also be applied to other data types.

For class arrays though, if there are fewer items in the initializer list than elements in the array, the default constructor is used for the remaining elements. If no default constructor is defined for the class, the initializer list must be complete — that is, there must be one initializer for each element in the array.

Answer 4

You can declare the array in C++ in these type of ways. If you know the array size then you should declare the array for: integer: int myArray[array_size]; Double: double myArray[array_size]; Char and string : char myStringArray[array_size]; The difference between char and string is as follows

char myCharArray[6]={'a','b','c','d','e','f'};
char myStringArray[6]="abcdef";

If you don't know the size of array then you should leave the array blank like following.

integer: int myArray[array_size];

Double: double myArray[array_size];

Answer 5

Additionally, keep a note of how the array and vector are default initialized if don't initialize them explicitly.

int main()
{
    bool arr1[3];                   // true  true  true  [here true is SOME garbage value] 
    std::vector<bool> vec1(3);      // false false false

    bool arr2[3] = { true };        // true false false [here true/false are REAL true/false values] 
    vector<bool> vec2(3, true);     // true true  true

    bool arr3[3] = { false };         // false false false
    std::vector<bool> vec3(3, false); // false false false


    int arr4[3];                      // GV GV GV - garbage value
    std::vector<int> vec4(3);         // 0 0 0

    int arr5[3] = { 1 };              // 1 0 0
    std::vector<int> vec5(3, 1);      // 1 1 1

    int arr6[3] = { 0 };              // 0 0 0
    std::vector<int> vec6(3, 0);      // 0 0 0
}