在C中，未初始化的布尔数组的默认值是多少？

I have something like,

我有类似的东西,

#include <stdio.h>
#include <stdbool.h>

int main()
{
    int t,answer;
    bool count;
    long long int L;
    scanf("%d",&t);
    while(t>0)
    {
        answer = 0;
        scanf(" %lld",&L);
        bool count[L];
  //  .....restofthecode. NDA Constraint.

What would be the default value of all the elements of arr[x]? Is it false always? Or true? Or any random value?

arr [x]的所有元素的默认值是什么?这总是假的吗?还是真的?或任何随机值?

2 个解决方案

#1

There is no type named boolean in C but there is _Bool and in stdbool.h a macro bool that expands to _Bool.

在C中没有名为boolean的类型,但是有_Bool,在stdbool.h中有一个扩展为_Bool的宏bool。

#include <stdbool.h>

#define X 42
bool arr[X];

arr elements have an initial value of false (that is 0) if declared at file scope and indeterminate if declared at block scope.

如果在文件范围内声明,则arr元素的初始值为false(即0),如果在块作用域中声明则不确定。

At block scope, use an initializer to avoid the indeterminate value of the elements:

在块作用域中,使用初始值设定项来避免元素的不确定值:

void foo(void)
{
     bool arr[X] = {false};  // initialize all elements to `false`
}

EDIT:

Now the question is slightly different:

现在问题略有不同:

long long int x;
scanf("%lld",&x);
bool arr[x];

This means arr is a variable length array. VLA can only have block scope, so like any object at block scope it means the array elements have an indeterminate value. You cannot initialize a VLA at declaration time. You can assign a value to the array elements for example with = operator or using memset function.

这意味着arr是一个可变长度数组。 VLA只能有块作用域,因此与块作用域中的任何对象一样,这意味着数组元素具有不确定的值。您无法在申报时初始化VLA。您可以为数组元素赋值,例如使用=运算符或使用memset函数。

#2

As per your code, in local scope

根据您的代码,在本地范围内

boolean arr[x];

itself is invalid. x is used uninitialized.

本身无效。 x未使用初始化。

Just FYI, in global [file] scope, all the variables are initialized to 0. In local scope, they simply contain garbage, unless initialized explicitly.

只是FYI,在全局[file]范围内,所有变量都初始化为0.在本地范围内,它们只包含垃圾,除非明确初始化。

---

EDIT:

[After the edit] All the variables in the arr array will have garbage value. It is in local scope [auto].

[编辑后] arr数组中的所有变量都将具有垃圾值。它在本地范围[auto]。