C++文件 输入时数字中掺杂字母

//L7_F0_P3.cpp #include <iostream> #include <fstream> using namespace std; int main() { ifstream ifs("L7_F0_P1.txt"); if( !ifs ) { cout << "Error opening file\n"; return 1; } int number; while( ifs >> number ) { // reading all numbers – number by number and cout << number << endl; // writing them to the standard output } ifs.close(); return 0; }

Question(b):

When ifs >> number is true, and when it is false?      

Answer(b):

ifs >> number is evaluated to true, when program correctly read a value of variable number (input data could be interpreted as some value of the appropriate type). On the other hand ifs >> number evaluates to false, when program cannot interpret the input data as a value that could be assigned to variable number or the end of file was reached, or there were some error.

Question(c):

Modify L7_F0_P1.txt such that it looks as follows 463 859A203 20 (replace space between 859 and

203 with letter A). What is the output of our program and why?

Answer(c):

There will be the two numbers in the output, i.e., 463 and 859. Then the next attempt to read from ifs results in ifs >> number evaluated to false and end of the while loop.