C++ ios::in|ios::out 是什么？
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What is ios::in|ios::out?
提问by Prakhar Verma
I was reading some project code and I found this,here MembersOfLibrary() is a constructor of class MenberOfLibrary
我正在阅读一些项目代码，我发现了这个，这里 MemberOfLibrary() 是类 MenberOfLibrary 的构造函数
class MembersOfLibrary {
public:
MembersOfLibrary();
~MembersOfLibrary() {}
void addMember();
void removeMember();
unsigned int searchMember(unsigned int MembershipNo);
void searchMember(unsigned char * name);
void displayMember();
private:
Members libMembers;
};
MembersOfLibrary::MembersOfLibrary() {
fstream memberData;
memberData.open("member.txt", ios::in|ios::out);
if(!memberData) {
cout<<"\nNot able to create a file. MAJOR OS ERROR!! \n";
}
memberData.close();
}
I m not able to understand the meaning of --> ios::in|ios::out <-- Please Help out ! Thank You
我无法理解 --> ios::in|ios::out <-- 请帮忙！谢谢你
采纳答案by emlai
ios::inallows input (read operations) from a stream.ios::outallows output (write operations) to a stream.|(bitwise OR operator) is used to combine the twoiosflags,
meaning that passingios::in | ios::outto the constructor
ofstd::fstreamenables bothinput and output for the stream.
ios::in允许来自流的输入（读取操作）。ios::out允许输出（写操作）到流。|（位或运算符）被用来在两个结合ios的标志，
这意味着通过ios::in | ios::out给构造
的std::fstream能够既用于流输入和输出。
Important things to note:
需要注意的重要事项：
std::ifstreamautomatically has theios::inflag set.std::ofstreamautomatically has theios::outflag set.std::fstreamhas neitherios::inorios::outautomatically
set. That's why they're explicitly set in your example code.
std::ifstream自动ios::in设置了标志。std::ofstream自动ios::out设置了标志。std::fstream没有ios::in或ios::out自动
设置。这就是它们在您的示例代码中明确设置的原因。
回答by Arun A S
memberData.open("member.txt", ios::in|ios::out);
ios::in is used when you want to read from a file
ios::in 用于读取文件
ios::out is used when you want to write to a file
ios::out 用于写入文件
ios::in|ios::out means ios::in or ios::out, that is whichever is required is used
ios::in|ios::out 表示 ios::in 或 ios::out，以需要的为准
Here's a useful link
这是一个有用的链接
回答by π?ντα ?ε?
ios::inand ios::outare openmode flags, and in your case combined with a binary or(|) operation. Thus the file is opened for reading and writing.
ios::in和ios::out是openmode flags，在您的情况下与二进制或( |) 操作相结合。因此文件被打开用于读取和写入。
