[英]c++ how to create std::string containing size uninitialized bytes?
i need a std::string of size
bytes, after constructing it i am going to write to every byte in that string prior to reading from it, thus null-initializing the string is a waste of cpu, this works:我需要一个
size
字节的std :: string,在构造它之后我将在读取它之前写入该字符串中的每个字节,因此对字符串进行空初始化是浪费cpu,这有效:
std::string s(size,0);
but it's just slightly wasteful, it's basically like using calloc()
when all i need is malloc()
, so the question is, how do i construct a string of X uninitialized bytes?但这只是有点浪费,基本上就像在我只需要
malloc()
calloc()
一样,所以问题是,我如何构造一串 X 未初始化字节?
(using reserve()+push is not an option because im giving the string to a C-api taking char*,size
to do the actual initialization) (使用reserve()+push 不是一个选项,因为我将字符串提供给C-api 使用
char*,size
来进行实际初始化)
edit: this thread seems to about the same issue/related (but with vectors instead of strings): Value-Initialized Objects in C++11 and std::vector constructor编辑:这个线程似乎与相同的问题/相关(但使用向量而不是字符串): C++11 和 std::vector 构造函数中的值初始化对象
You can't do it with std::string
.你不能用
std::string
做到这一点。 But it can be achieved different way, like using std::unique_ptr<char[]>
.但它可以通过不同的方式实现,例如使用
std::unique_ptr<char[]>
。
auto pseudo_string = std::unique_ptr<char[]>(new char[size]);
Or if your compiler supports C++20或者,如果您的编译器支持 C++20
auto pseudo_string = std::make_unique_for_overwrite<char[]>(size);
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