C++ 正确读取和写入 std::vector 到文件中
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Reading and writing a std::vector into a file correctly
提问by FacundoGFlores
That is the point. How to write and read binary files with std::vector inside them?
这就是我想说的。如何使用 std::vector 写入和读取二进制文件？
I was thinking something like:
我在想这样的事情：
//============ WRITING A VECTOR INTO A FILE ================
const int DIM = 6;
int array[DIM] = {1,2,3,4,5,6};
std::vector<int> myVector(array, array + DIM);
ofstream FILE(Path, ios::out | ofstream::binary);
FILE.write(reinterpret_cast<const char *>(&myVector), sizeof(vector) * 6);
//===========================================================
But I don't know how to read this vector. Because I thought that the following was correctly but it isn't:
但我不知道如何阅读这个向量。因为我认为以下是正确的，但事实并非如此：
ifstream FILE(Path, ios::in | ifstream::binary);
FILE.read(reinterpret_cast<const char *>(&myVector), sizeof(vector) * 6);
So, how to perform the operation?
那么，如何进行操作呢？
回答by Platinum Azure
Try using an ostream_iterator/ostreambuf_iterator, istream_iterator/istreambuf_iterator, and the STL copymethods:
尝试使用ostream_iterator/ ostreambuf_iterator、istream_iterator/istreambuf_iterator和 STLcopy方法：
#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
#include <fstream> // looks like we need this too (edit by π)
std::string path("/some/path/here");
const int DIM = 6;
int array[DIM] = {1,2,3,4,5,6};
std::vector<int> myVector(array, array + DIM);
std::vector<int> newVector;
std::ofstream FILE(path, std::ios::out | std::ofstream::binary);
std::copy(myVector.begin(), myVector.end(), std::ostreambuf_iterator<char>(FILE));
std::ifstream INFILE(path, std::ios::in | std::ifstream::binary);
std::istreambuf_iterator iter(INFILE);
std::copy(iter.begin(), iter.end(), std::back_inserter(newVector));
回答by ForEveR
Use boost::serialization.
使用boost::serialization.
If you don't want use boost- write size and vector.
如果您不想使用boost- 写入大小和vector.
size_t sz = myVector.size();
FILE.write(reinterpret_cast<const char*>(&sz), sizeof(sz));
FILE.write(reinterpret_cast<const char*>(&myVector[0]), sz * sizeof(myVector[0]));
回答by piokuc
You can use
您可以使用
#include <boost/serialization/vector.hpp>
to serialize your vector. Read a tutorial here: http://www.boost.org/libs/serialization/doc/tutorial.html#stl`
序列化您的向量。在此处阅读教程：http: //www.boost.org/libs/serialization/doc/tutorial.html#stl`
回答by Igor R.
Before reading vector, you should resize it: yourVector.size(numberOfElementsYouRead).
阅读之前vector，你应该调整它：yourVector.size(numberOfElementsYouRead)。
Besides, sizeof(vector<your_type>)is just the size of the vectorobject internal implementation; vector element size is sizeof(std::vector<your_type>::value_type).
此外，sizeof(vector<your_type>)只是vector对象内部实现的大小；向量元素大小为sizeof(std::vector<your_type>::value_type)。
Then read it like this:
然后像这样阅读它：
file.read(reinterpret_cast<char *>(&myVector[0]), sizeof(vector<int>::element_type) * element_count);
回答by Jan
I used the fact that the data() method returns an address you can use for reading AND for writing.
我使用了 data() 方法返回一个可用于读取和写入的地址的事实。
// Assume outf is a writable filepointer (binary). // write myVector.size() to file, then
// 假设 outf 是一个可写的文件指针（二进制）。// 将 myVector.size() 写入文件，然后
fwrite(myVector.data(), sizeof(decltype(myVector)::value_type), myVector.size(), outf);
to read:
阅读：
// read MyVector.size() from file as nv, inpf is read filepointer
// 从文件中读取 MyVector.size() 作为 nv，inpf 是读取文件指针
MyVector.resize(nv);
fread(MyVector.data(), sizeof(decltype(MyVector)::value_type), nv, inpf);
clinging to old ways in file io, but please ignore that (even if it might irritate you :)).
坚持文件 io 中的旧方法，但请忽略它（即使它可能会激怒你:)）。
A weakness is that endianness is unsupported in this way.
一个弱点是这种方式不支持字节顺序。
