C ++浮点数组初始化 [英] C++ float array initialization

问题描述

可能重复：

C和C ++：自动结构的部分初始化

在阅读完整代码时，我遇到了一个C ++数组初始化的例子：

  float studentGrades [MAX_STUDENTS] = {0.0}; 
  

我不知道C ++可以初始化整个数组，所以我测试了它：

  #include< iostream> 
使用namespace std; 
 
 int main（）{
 const int MAX_STUDENTS = 4; 
 float studentGrades [MAX_STUDENTS] = {0.0}; 
 for（int i = 0; i  cout<<我 << studentGrades [i]<< \\\
; 
} 
 return 0; 
 
 $ / code> 

该程序给出了预期的结果：



  0 0 
 1 0 
 2 0 
 3 0 
  

$ b $

但是将初始化值从 0.0 更改为 9.9 ：

  float studentGrades [MAX_STUDENTS] = {9.9}; 
  

给出了有趣的结果：

  0 9.9 
 1 0 
 2 0 
 3 0 
  

初始化声明是否只设置数组中的第一个元素？

解决方案

那么你只能将前N个位置初始化为该值，而其他所有的位置初始化为0.在这种情况下，N是你传递给初始化列表的参数个数，即

  float arr1 [10] = {}; //所有的元素都是0 
 float arr2 [10] = {0}; //所有元素都是0 
 float arr3 [10] = {1}; //第一个元素是1，其他元素都是0 
 float arr4 [10] = {1,2}; //第一个元素是1，第二个元素是2，其他元素都是0 
  

Possible Duplicate:
C and C++ : Partial initialization of automatic structure

While reading Code Complete, I came across an C++ array initialization example:

float studentGrades[ MAX_STUDENTS ] = { 0.0 };

I did not know C++ could initialize the entire array, so I've tested it:

#include <iostream>
using namespace std;

int main() {
    const int MAX_STUDENTS=4;
    float studentGrades[ MAX_STUDENTS ] = { 0.0 };
    for (int i=0; i<MAX_STUDENTS; i++) {
        cout << i << " " << studentGrades[i] << '\n';
    }
    return 0;
}

The program gave the expected results:

0 0
1 0
2 0
3 0

But changing the initialization value from 0.0 to, say, 9.9:

float studentGrades[ MAX_STUDENTS ] = { 9.9 };

Gave the interesting result:

0 9.9
1 0
2 0
3 0

Does the initialization declaration set only the first element in the array?

解决方案

If you use anything but empty braces then you only initialize the first N positions to that value and all others are initialized to 0. In this case, N is the number of arguments you passed to the initialization list, i.e.,

float arr1[10] = { };       // all elements are 0
float arr2[10] = { 0 };     // all elements are 0
float arr3[10] = { 1 };     // first element is 1, all others are 0
float arr4[10] = { 1, 2 };  // first element is 1, second is 2, all others are 0

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