使用 C++ 写入文件杜普2
好吧，我正在尝试从一个文件读取并写入另一个文件。
我还有其他需要添加的内容，例如从第一个文件中获取信息，但为了测试我试图将其写入第二个文件。
我的理解是 dp2() 调用之后的所有内容都会输出到第二个参数。正确的？
using namespace std;
using std::string;
using std::ostream;
using std::endl;
string str;
int main(){
int file= open("./input.txt", O_CREAT | O_RDWR | O_APPEND, S_IRUSR | S_IWUSR);
if(file==-1){
cout<<"Error: "<<errno<<endl;
}
int file2= open("./output.txt", O_CREAT | O_RDWR | O_APPEND, S_IRUSR | S_IWUSR);
if(file2==-1){
cout<<"Error: "<<errno<<endl;
}
int retval = dup2(file,file2);
if(retval == -1){
cout<<"Error: "<<errno;
}
printf("yeah");
close(file);
}
Alright I am trying to read from one file and write to another.
I have other things to add such as grabbing info from the first file but for testing I am trying to get it to write to the second file.
My understanding was that everything after the dp2() call would output to the second param. Right?
using namespace std;
using std::string;
using std::ostream;
using std::endl;
string str;
int main(){
int file= open("./input.txt", O_CREAT | O_RDWR | O_APPEND, S_IRUSR | S_IWUSR);
if(file==-1){
cout<<"Error: "<<errno<<endl;
}
int file2= open("./output.txt", O_CREAT | O_RDWR | O_APPEND, S_IRUSR | S_IWUSR);
if(file2==-1){
cout<<"Error: "<<errno<<endl;
}
int retval = dup2(file,file2);
if(retval == -1){
cout<<"Error: "<<errno;
}
printf("yeah");
close(file);
}
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评论（1）
首先，我不确定是什么让您相信您需要使用
dup2()。不要在这里使用它，它不是必需的，而且会做错误的事情。其次，要将输出写入低级文件描述符，请使用 write()：
完成后不要忘记 close(file2)。
First, I'm not sure what led you to believe that you need to use
dup2(). Don't use it here, it's not needed and will do the wrong thing.Second, to write output to a low-level file descriptor, use
write():Don't forget to
close(file2)when you're done with it.