File Input from structue???

I have a quick question about inputting data. More specifically data that is of the fallowing struct

Code:

enum sex {male, female};

struct data
{
	char name[30];
	sex MF;
	int age;
	double weight;
};

Some one has asked me for some help with this but I cant seem to work out how to input the data from this file. if anyone wants to view the file. I have been told that its formatted as per the above structure.

All of the input and output I have always uses was using the fallowing method.

Code:

FILE *input;  // declare a pointer of type FILE
char buffer[400];  // a buufer array
input=fopen("C:\\Sales.txt","r");  // opens file
read(buffer,1,200,input);  // read 200 characters to buffer

Is there someway to use the above method? Or is there an alternative?

Perhaps
struct data student;
fread( &student, sizeof student, 1, input );

Though you will need to open the file with "rb" mode.

You also need to know that reading a binary file in unportable in a large number of ways.
- structure padding and alignment varies between compilers.
- endian-ess and data type sizes vary from machine to machine.
To counteract all these issues, you would have to read the file one byte at a time.

This will work. I don't know how to do it using c++ streams though. You have to open the file in binary mode and read a chunk of data the size of your structure. If you pass fread() a pointer to your structure it will populate your structure (assuming the file has the correct format).

Code:

int main(int argc, char *argv[])
{
    FILE * sFile;
    struct data student[10];
    
    if (NULL == (sFile = fopen("student.data", "rb")))
    {
        cout << "Could not open file" << endl;
        system("PAUSE");
        return -1;
    }
    cout << "name\tsex\tage\tweight:" << endl;
    for (int i=0; i<10; i++)
    {
        fread(&student[i], sizeof(data), 1, sFile);
        cout << student[i].name << "\t";
        student[i].MF?(cout << "female\t"):(cout << "male\t");     
        cout << student[i].age << "\t" << student[i].weight << endl;
    }
    system("PAUSE");
    return EXIT_SUCCESS;
}

kyle

A structure can be read by writing your own operator>> and operator<< functions that takes that structure as an argument (and a istream/ostream as well, of course).

You can use >> and << inside the structure reading function, if that's what you want to do.

Note that this will read/write data in text form (assuming you use the >>/<< operators), not in binary form like the fread/fwrite functions do - there are good and bad things about that.


If you want to use binary form, use the fstream::read and fstream::write
http://www.cplusplus.com/reference/i...ream/read.html
http://www.cplusplus.com/reference/i...eam/write.html

--
Mats

Thanks for the info. So heres the revised example which contains both the c method and the c++ file stream method:

Code:

#define USE_STREAMS

enum sex {male, female};
struct data
{
	char name[30];
	sex MF;
	int age;
	double weight;
};

using namespace std;
int main(int argc, char *argv[])
{
    int length;
    struct data student[10];
    
    #ifdef USE_STREAMS
    ifstream isFile;
    isFile.open ("student.data", ios::binary );

    isFile.seekg (0, ios::beg);
    // read data 
    for (int i=0; i<10; i++)
    {            
        isFile.read ((char *)(&student[i]),sizeof(data));
    }
    isFile.close();
    cout << "name\tsex\tage\tweight:" << endl;
    for (int i=0; i<10; i++)
    {
        cout << student[i].name << "\t";
        student[i].MF?(cout << "female\t"):(cout << "male\t");     
        cout << student[i].age << "\t" << student[i].weight << endl;
    }
    #else
    FILE * sFile;
     
    if (NULL == (sFile = fopen("student.data", "rb")))
    {
        cout << "Could not open file" << endl;
        system("PAUSE");
        return -1;
    }
    cout << "name\tsex\tage\tweight:" << endl;
    for (int i=0; i<10; i++)
    {
        fread(&student[i], sizeof(data), 1, sFile);
        cout << student[i].name << "\t";
        student[i].MF?(cout << "female\t"):(cout << "male\t");     
        cout << student[i].age << "\t" << student[i].weight << endl;
    }
    #endif //USE_STREAMS
    system("PAUSE");
    return EXIT_SUCCESS;
}

kyle

Code:

student[i].MF?(cout << "female\t"):(cout << "male\t");

Seems to me that this would be simpler:

Code:

cout << (student[i].MF ? "female : "male") << '\t';

Also note that you'd need to include <fstream> for the streams version and <cstdio> for the C version.