Question

我想用相同的值填充MyStruct数组。如何以最快和最简单的方式完成？我正在运行相当低级的方法，例如memset或memcpy。

编辑：std::fill_n确实符合并且正常工作。但它是C ++的方式。 如何在纯C中完成？

struct MyStruct
{
    int a;
    int b;
};

void foo()
{
    MyStruct abc;
    abc.a = 123;
    abc.b = 321;

    MyStruct arr[100];
    // fill 100 MyStruct's with copy of abc
    std::fill_n(arr, 100, abc); // working C++ way

    // or maybe loop of memcpy? But is it efficient?
    for (int i = 0; i < 100; i++)
        memcpy(arr[i],abc,sizeof(MyStruct));
}

Answer 1

注意正确键入类型的名称（区分大小写）并且在struct定义后不要忘记分号，除此之外，您的程序应该编译没有问题：

#include <iostream>
#include <algorithm>

struct MyStruct
{
    int a;
    int b;
}; // <------------- HERE

int main() {
    MyStruct abc;
    abc.a = 123;
    abc.b = 321;

    MyStruct arr[100];
    std::fill_n(arr, 100, abc);

    std::cout << arr[99].b;
}

输出321。

“如何以最快最简单的方式完成？”

最简单的方法可能是使用std::vector及其相应的构造函数：

#include <vector>

void foo()
{
    MyStruct abc;
    abc.a = 123;
    abc.b = 321;

    std::vector<MyStruct> vec(100, abc);
    ...
}

Answer 2

for(int i = 0; i < 100; i++)
{
    arr[i] = abc;
}

最快，最干净。优化器很可能也很有效。

Answer 3

以下内容适用于C

MyStruct arr[100] = {
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},
   {123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321},{123,321}};

Answer 4

不是纯粹的C，但是GCC允许你很好地完成它：

MyStruct arr[100] = { [ 0 ... 99 ] = { .a = 123, .b = 321 } };

如果您需要纯C，我会follow Tri-Edge Al's answer。

Answer 5

我对C99的猜测将低于代码：

#include <stdio.h>

typedef struct MyStruct
{
    int a ;
    int b ;
} MyStruct_t;

const MyStruct_t abc = 
{
    .a = 0,
    .b = 321, 
};

void main(void)
{
    int i = 0 ;

    MyStruct_t arr[100] = {0} ;

    for(i=0 ;i <sizeof(arr)/sizeof(arr[0]);i++)
    {
        arr[i] = abc ;
    }
}

在我看来，这是最清洁，最安全的解决方案。

C / C ++用一个值填充struct数组

5 个答案: