从一个动态分配的数组复制到另一个 C++
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原文地址: http://stackoverflow.com/questions/8056746/
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Copying from One Dynamically Allocated Array to Another C++
提问by Rahul Gupta-Iwasaki
This seems like it should have a super easy solution, but I just can't figure it out. I am simply creating a resized array and trying to copy all the original values over, and then finally deleting the old array to free the memory.
这似乎应该有一个超级简单的解决方案，但我就是想不通。我只是创建一个调整大小的数组并尝试复制所有原始值，然后最后删除旧数组以释放内存。
void ResizeArray(int *orig, int size) {
int *resized = new int[size * 2];
for (int i = 0; i < size; i ++)
resized[i] = orig[i];
delete [] orig;
orig = resized;
}
What seems to be happening here is that resized[i] = orig[i]is copying values by reference rather than value, as printing orig after it gets resized returns a bunch of junk values unless I comment out delete [] orig. How can I make a deep copy from orig to resized, or is there some other problem that I am facing? I do not want to use std::vector.
这里似乎发生的是resized[i] = orig[i]通过引用而不是值复制值，因为在调整大小后打印原稿会返回一堆垃圾值，除非我注释掉delete [] orig. 如何从 orig 进行深层复制以调整大小，或者我面临其他一些问题？我不想使用 std::vector。
回答by Matteo Italia
Remember, parameters in C++ are passed by value. You are assigning resizedto a copyof the pointer that was passed to you, the pointer outside the function remains the same.
请记住，C++ 中的参数是按值传递的。您正在分配传递给您的指针resized的副本，函数外的指针保持不变。
You should either use a double indirection (or a "double pointer", i.e. a pointer to a pointer to int):
您应该使用双间接寻址（或“双指针”，即指向指向的指针int）：
void ResizeArray(int **orig, int size) {
int *resized = new int[size * 2];
for (int i = 0; i < size; i ++)
resized[i] = (*orig)[i];
delete [] *orig;
*orig = resized;
}
or a reference to the pointer:
或对指针的引用：
void ResizeArray(int *&orig, int size) {
int *resized = new int[size * 2];
for (int i = 0; i < size; i ++)
resized[i] = orig[i];
delete [] orig;
orig = resized;
}
By the way, for array sizes you should use the type std::size_tfrom <cstddef>- it is guaranteed to hold the size for any object and makes clear that we are dealing with the size of an object.
顺便说一下，对于数组大小，您应该使用std::size_tfrom类型<cstddef>- 它保证保存任何对象的大小，并明确我们正在处理对象的大小。
回答by Thomas Matthews
I highly suggest replacing the arrays with std::vector<int>. This data structure will resize as needed and the resizing has already been tested.
我强烈建议用std::vector<int>. 此数据结构将根据需要调整大小，并且调整大小已经过测试。
回答by Drew
origmust be a pointer to a pointer to assign it to resized:
orig必须是指向要分配给的指针的指针resized：
int **orig;
*orig = resized;
