c++怎么把一个类的数组 写入一个文件 打开的时候再读出来

Use

#include 
// ofstream to either read from or write in the file
ofstream write_in ( const char*, ios::app )

Initialize obj_t when class T only is called the fixed times

class T {} obj_t;

Test wether the file in `path_out` is opened or not for the safety consideration

write_in.is_open()

The sample solution of your question should look like below

#include 
#include 

using namespace std;

const char* path_out = "data.txt";

class FF {
	public:
		int id = 10086;
		char name[12] = "xxx xxx";
		int price = 0;
} obj_FF;

ofstream write_in ( path_out, ios::app );

bool is_open( const char* path ) {
	if ( !write_in.is_open() ) return false;
	return true;
}

int main(int argc, char *argv[]) {
	
	if ( is_open(path_out) ) {

		
		write_in.close();
	}
}

Notice the saved data file is under the same directory of your main.cpp file when the variable `path_out` is not specified, which is also shown below.

问题很白痴