[英]Return an array pointer from a function with non-constant array size in C++
I built a function to generate a random 2-d array in C++. 我构建了一个函数来在C ++中生成随机的二维数组。 I was hoping that I could set the size of the array at compile time, so I included variables for the number of rows and columns in the array.
我希望可以在编译时设置数组的大小,因此我在数组中包含了行和列数的变量。 However, when I try to compile the function, I get an error about the storage size of the array is not constant.
但是,当我尝试编译该函数时,出现关于数组的存储大小不是恒定的错误。 This seems to do with the the
static
keyword that I have to add to the array definition, so that I can return the pointer from the function. 这似乎与我必须添加到数组定义中的
static
关键字有关,以便可以从该函数返回指针。 I was not sure if there is a way around this error? 我不确定是否有解决此错误的方法? Any suggestions.
有什么建议么。
double * generate_random_array(int rows, int cols, double lower_, double upper_){
static double test_array[rows][cols];
for (int i = 0; i < sizeof test_array / sizeof test_array[0]; i++) {
for (int j = 0; j < sizeof test_array[0] / sizeof(double); j++) {
test_array[i][j] = generate_random_numbers(lower_, upper_);
}
}
return(test_array);
}
You can make generate_random_array
a template
, enforcing rows
and cols
to be known at compile-time: 您可以
generate_random_array
一个template
,执行rows
和cols
在编译时被称为:
template <int rows, int cols>
double* generate_random_array(double lower_, double upper_)
{
/* ... as before ... */
}
Example usage: 用法示例:
generate_random_array<5, 10>(51.4, 66.0);
Nevertheless, you should use std::array
instead of C-style arrays. 不过,您应该使用
std::array
而不是C样式的数组。 If you want resizable arrays, then you should use std::vector
instead. 如果要调整数组的大小,则应改用
std::vector
。
std::array
example: std::array
示例:
template <int rows, int cols>
auto generate_random_array(double lower_, double upper_)
{
const auto idx = [](int x, int y){ return y * rows + x; };
std::array<double, rows * cols> result;
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
result[idx(i, j)] = generate_random_numbers(lower_, upper_);
}
}
return result;
}
Example usage: 用法示例:
auto test_array = generate_random_array<5, 10>(11.0, 66.33);
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