Wednesday evening, August 2, 2023
Today I saw these two lines of code:
std::ofstream file("example.txt", std::ios_base::out);
std::ofstream file("example.txt", std::ios::out);
This raised a few questions for me:
Why do I sometimes use ios_base::out and sometimes ios::out?
Is there a difference between ios_base::out and ios::out?
It took me an hour or two to figure it out....
Table of contents
- in conclusion
- What are the I/O flow control flags of the ios_base class?
- What are the I/O flow control flags of the iOS class?
- prove that they are the same
in conclusion
There is no difference between ios_base::out and ios::out, they are exactly the same.
Because they are all integer constants and have the same values, they can completely replace each other.
As for when to use which one, I think use whichever one you like because they are really the same.
What are the I/O flow control flags of the ios_base class?
std::ios_base::in: Input mode, indicating that the stream is opened in reading mode.std::ios_base::out: Output mode.std::ios_base::app: Append mode, which means opening the stream in writing mode and appending data to the end of the file without clearing the original content.std::ios_base::trunc: Truncate mode, which means opening the stream in writing mode and clearing the original content of the file.std::ios_base::binary: Binary mode, open the stream in binary mode.std::ios_base::ate: Position the file pointer to the end of the file after opening the stream.
What are the I/O flow control flags of the iOS class?
std::ios::in: Input mode, indicating that the stream is opened in reading mode.std::ios::out: Output mode.std::ios::app: Append mode, which means opening the stream in writing mode and appending data to the end of the file without clearing the original content.std::ios::trunc: Truncate mode, which means opening the stream in writing mode and clearing the original content of the file.std::ios::binary: Binary mode, open the stream in binary mode.std::ios::ate: Position the file pointer to the end of the file after opening the stream.
prove that they are the same
#include<iostream>
#include<fstream>
int main(){
printf("ios_base::in的值：%d\n",std::ios_base::in);
printf("ios::in的值：%d\n",std::ios::in);
printf("-------------\n");
printf("ios_base::out的值：%d\n",std::ios_base::out);
printf("ios::out的值：%d\n",std::ios::out);
printf("-------------\n");
printf("ios_base::app的值：%d\n",std::ios_base::app);
printf("ios::app的值：%d\n",std::ios::app);
printf("-------------\n");
printf("ios_base::trunc的值：%d\n",std::ios_base::trunc);
printf("ios::trunc的值：%d\n",std::ios::trunc);
printf("-------------\n");
printf("ios_base::binary的值：%d\n",std::ios_base::binary);
printf("ios::binary的值：%d\n",std::ios::binary);
printf("-------------\n");
printf("ios_base::ate的值：%d\n",std::ios_base::ate);
printf("ios::ate的值：%d\n",std::ios::ate);
printf("-------------\n");
}