[英]C++: How do you pass a file as an argument?
I initialized and opened a file in one of the functions and I am supposed to output data into an output file.我在其中一个函数中初始化并打开了一个文件,我应该将 output 数据放入 output 文件中。 How can I pass the file as an argument so that I can output the data into the same output file using another function?如何将文件作为参数传递,以便可以使用另一个 output 将数据放入同一个 output 文件中,使用另一个 function? For example:例如:
void fun_1 () {
ifstream in;
ofstream outfile;
in.open("input.txt");
out.open("output.txt");
////function operates////
//........
fun_2()
}
void fun_2 () {
///// I need to output data into the output file declared above - how???
}
Your second function needs to take a reference to the stream as an argument, ie,您的第二个 function 需要引用 stream 作为参数,即
void fun_1 ()
{
ifstream in;
ofstream outfile;
in.open("input.txt");
out.open("output.txt");
fun_2( outfile );
}
void fun_2( ostream& stream )
{
// write to ostream
}
Pass a reference to the stream:传递对 stream 的引用:
void first() {
std::ifstream in("in.txt");
std::ofstream out("out.txt");
second(in, out);
out.close();
in.close();
}
void second(std::istream& in, std::ostream& out) {
// Use in and out normally.
}
You can #include <iosfwd>
to obtain forward declarations for istream
and ostream
, if you need to declare second
in a header and don't want files that include that header to be polluted with unnecessary definitions.如果您需要在 header 中声明second
个并且不希望包含该 header 的文件被不必要的定义污染,您可以#include <iosfwd>
获取istream
和ostream
的前向声明。
The objects must be passed by non- const
reference because insertion (for output streams) and extraction (input) modify the stream object.对象必须通过非const
引用传递,因为插入(对于 output 流)和提取(输入)会修改 stream object。
Pass a reference to the stream.传递对 stream 的引用。
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