使用从文件读取的结构的函数没有输出吗？

Question

I am supposed to declare a structure that holds the name and grades of an unknown number of students. Here is how I did it:

struct student {
    char name[30];
    int grade1, grade2, grade3;
};

Then, I have a text file containing the information for each student on different lines. I read it this way.

student info[20];
int nr_students,i=0,k=0;
fstream inFile;
inFile.open("in.txt");
fstream outFile;
outFile.open("out.txt");

while(!EOF) {
    inFile>>info[i].name;
    inFile>>info[i].grade1;
    inFile>>info[i].grade2;
    inFile>>info[i].grade3;
    i++;

}
nr_students=i;
avg_promovability(outFile,info, nr_students);

I do not think this works properly, since the nr_students remains 0, apparently. Also, the first function:

void avg_promovability(fstream &outFile,student *info, int nr_students)
{
    int i;
    float sum=0,j=0,avg;
    for (i=0;i<nr_students;i++)
        if(info[i].grade1 >=5 && info[i].grade2>=5 && info[i].grade3>=5 ) {
            sum=sum + info[i].grade1 + info[i].grade2 + info[i].grade3;
            j++;
        }
    avg=sum/(3*j);
    outFile<<avg;

}

It's supposed to calculate the average grade of the students that have passed (that is, all their grades are >=5). It doesn't really do it, the out.txt file is always empty. Any suggestions as to what I'm doing wrong?

Answer 1

That is not the way you check for the end of the file. Try

while (inFile>>info[i].name) {
     inFile>>info[i].grade1;
     inFile>>info[i].grade2;
     inFile>>info[i].grade3;
     i++;
}

Answer 2

The core problem of not reading the student info has been pointed out by the answer by @VaughnCato.

Additionally...

Since you are using C++, I think you should use an std::vector<student> to hold the information of all students. Then, you don't need to worry about counting the number of students and keeping track of them in nr_students .

Then you can change the signature of avg_promovability from

void avg_promovability(fstream &outFile,student *info, int nr_students) 

to

void avg_promovability(fstream &outFile, std::vector<student> const& info) 

Answer 3

I would recommend overloading the extraction operator, >>, and assignment operator, =, to take in the name and three grades of the temporary student and assign it to the array.

Then..

while(inFile >> student) {
   info[i] = student;
   i++;
}

This will ensure there are no errors that slip by. This is probably better practice and will make debugging easier in case of seg faults.

erip

Answer 4

Try to replace this line of code

while(!EOF) {

with this

while(infile!=EOF) {