[英]Reading and writing a std::vector into a file correctly
That is the point. 这就是重点。 How to write and read binary files with std::vector inside them? 如何在其中写入和读取带有std :: vector的二进制文件?
I was thinking something like: 我想的是:
//============ 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. 但我不知道如何阅读这个载体。 Because I thought that the following was correctly but it isn't: 因为我认为以下是正确的,但它不是:
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?
Try using an ostream_iterator
/ ostreambuf_iterator
, istream_iterator
/ istreambuf_iterator
, and the STL copy
methods: 尝试使用ostream_iterator
/ ostreambuf_iterator
, istream_iterator
/ istreambuf_iterator
和STL copy
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));
Use boost::serialization
. 使用boost::serialization
。
If you don't want use boost
- write size and vector
. 如果你不想使用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]));
You can use 您可以使用
#include <boost/serialization/vector.hpp>
to serialize your vector. 序列化你的矢量。 Read a tutorial here: http://www.boost.org/libs/serialization/doc/tutorial.html#stl ` 在这里阅读教程: http : // www.boost.org/libs/ serialization/ doc/tutorial.html#stl`
Before reading vector
, you should resize it: yourVector.size(numberOfElementsYouRead)
. 在读取vector
之前,您应该调整它的大小: yourVector.size(numberOfElementsYouRead)
。
Besides, sizeof(vector<your_type>)
is just the size of the vector
object internal implementation; 此外, sizeof(vector<your_type>)
只是vector
对象内部实现的大小; vector element size is sizeof(std::vector<your_type>::value_type)
. 向量元素大小是sizeof(std::vector<your_type>::value_type)
。
Then read it like this: 然后像这样读:
file.read(reinterpret_cast<char *>(&myVector[0]), sizeof(vector<int>::element_type) * element_count);
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). //假设outf是一个可写的文件指针(二进制)。 // write myVector.size() to file, then //然后将myVector.size()写入文件
fwrite(myVector.data(), sizeof(decltype(myVector)::value_type), myVector.size(), outf);
to read: 读书:
// 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(即使它可能会刺激你:))。
A weakness is that endianness is unsupported in this way. 缺点是以这种方式不支持字节序。
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