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问题描述
在分配给动态分配的 std :: vector
的元素时,遇到了我认为基于c ++ 11范围的for循环很奇怪的行为。我有以下代码:
I have come across what I consider weird behaviour with the c++11 range-based for loop when assigning to elements of a dynamically allocated std::vector
. I have the following code:
int arraySize = 1000;
std::string fname = "aFileWithLoadsOfNumbers.bin";
CTdata = new std::vector<short int>(arraySize, 0);
std::ifstream dataInput(fname.c_str(), std::ios::binary);
if(dataInput.is_open()
{
std::cout << "File opened sucessfully" << std::endl;
for(auto n: *CTdata)
{
dataInput.read(reinterpret_cast<char*>(&n), sizeof(short int));
// If I do "cout << n << endl;" here, I get sensible results
}
// However, if I do something like "cout << CTdata->at(500) << endl;" here, I get 0
}
else
{
std::cerr << "Failed to open file." << std::endl;
}
如果我将循环更改为更传统的 for(int i = 0; i< arraySize; i ++)
并使用& CTdata-&at; at(i)
代替& n
在读取功能中,事情按预期执行。
If I change the loop to a more traditional for(int i=0; i<arraySize; i++)
and use &CTdata->at(i)
in place of &n
in the read function, things do as I would expect.
我缺少什么?
推荐答案
更改此循环语句
for(auto n: *CTdata)
至
for(auto &n : *CTdata)
那是您必须使用对向量元素的引用。
that is you have to use references to elements of the vector.
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