将.txt文件读入结构数组

Question

I'm a beginner in programming and i'm trying to read my.txt file into an array of struct in this program which after that display the data and then sort it, but the program only reads the first line and the loop won't stop until arraysize. The file data looks like this:

ID NAME ADDRESS AGE

The Code:

#include <iostream>
#include <fstream>
#include <string>
#include <conio.h>
using namespace std;

struct bio
{
    char name[50], address[50];
    int id, age; 
};

int main() 
{   
    int i = 0, arraysize = 1000;
    bio b[arraysize];
    fstream data;
    data.open("biodata.txt");
    while(data.read((char*)&b, sizeof(b[i])))
    {
        for (i = 1; i < 1000; i++)
        {
            data >> b[i].id >> b[i].name >> b[i].address >> b[i].age;
        }
    }
    for (i = 0; i < 1000; i++)
    {
        cout << b[i].id << " " << b[i].name << " " << b[i].address << " " << b[i].age << " " << endl;
    }
    data.close();
    getch();
}

Answer 1

#include <iostream>
#include <fstream>
#include <string>

#define ARRAY_SIZE 1000
#define FILE_NAME "biodata.txt"

using namespace std;

struct Bio
{
    int     m_id;
    string  m_name;
    string  m_address;
    int     m_age; 
};

int main() 
{ 
    Bio bio[ARRAY_SIZE];
    ifstream data;
    data.open(FILE_NAME);

    if (!data)
    {
        cout << "not file " << FILE_NAME;
        return 0;
    }

    for (int i = 0; i < ARRAY_SIZE && data.good(); ++i)
    {
        data >> bio[i].m_id >> bio[i].m_name >> bio[i].m_address >> bio[i].m_age;
    }

    for (int i = 0; i < ARRAY_SIZE ; ++i)
    {
        cout << bio[i].m_id << " " << bio[i].m_name << " " << bio[i].m_address << " " << bio[i].m_age << " " << endl;
    }

    data.close();
}

a few comments:

1. for what conio lib?
2. struct (bio) start with capital letter
3. don't use in char array in c++, you have string for this.
4. separate the variables to separate lines (bot "char name[50], address[50];")
5. better to rename members to m_X
6. about your "arraysize". if it const number you decide, do it with #define. if you need the whole file, you don't need it at all. (the file name too)
7. ifstream and not fstream data. you need just read. you don't want to change your data with some mistake.
8. check it the file opened well
9. in your code you check the while just before the loop.
10. in your condition loop check data.good(). it check it not eof and he file is readable.
11. read command is for binary file
12. it's better to separate the load file and print data to 2 differents functions. I didn't do it for save on your template

Answer 2

Assuming the file only contains the data for the bio array (ie it doesn' have a heading at the top), you're doing too many reads here:

 while(data.read((char*)&b, sizeof(b[i]))) { for (i = 1; i < 1000; i++) { data >> b[i].id >> b[i].name >> b[i].address >> b[i].age; } }

data.read() will read in a struct, so no need for data >> b[i].id etc.

Just change the loop to:

while (data.read((char*)&b[i], sizeof(bio)))
{
    i++;
}

to read in the data into the array element by element.

If, however, each bio data is on a separate line and white space separates each field refer to the other answer given by @gil.

Answer 3

The following is maybe a little complicated for beginners, but since we are talking about C++, we should look also to a "more" objective oriented approach.

You designed a class, called bio. In object oriented languages you will put all data for an object and also all functions that operate on this data in the class. So you need to add member functions. The idea is that you encapsulate all data in an object. The outside world should not know anything about the details of the class. You just access it via member functions. And if you want to make changes later than you will do this within the member functions of the classes. And the rest of the program will continue to work.

Additionally we should definitely use C++ language features. For examples you should use std::string for strings and not Plain old C-Style char arrays. You should basically never use C-Style arrays in C++. Instead, please use STL container.

So, then let's design a class with data members and member functions. Since at the moment we just need input and output functionality, we overwrite the inserter and extractor operator. These operators know abot the data and behaviour of the class and will take care.

See the following program:

#include <iostream>
#include <iterator>
#include <vector>
#include <algorithm>
#include <sstream>

struct Bio
{
    // Data
    unsigned int id{}; 
    std::string name{};
    std::string address{};
    unsigned int age{};

    // Overload extractor operator to read all data
    friend std::istream& operator >> (std::istream& is, Bio& b) {
        std::string textLine{};
        if (std::getline(is, textLine)) {
            std::istringstream textLineStream{textLine};
            textLineStream >> b.id >> b.name >> b.address >> b.age;
        }
        return is;
    }

    // Overload inserter operator to print the data 
    friend std::ostream& operator << (std::ostream& os, const Bio& b) {
        return os << b.id << " " << b.name << " " << b.address << " " << b.age;
    }
};

std::istringstream sourceFile{R"(1 John Address1 31
2 Paul Address2 32
3 Ringo Address3 33
4 George Address4 34
)"};

int main()
{
    // Define Variable and read complete source file
    std::vector<Bio> bio{std::istream_iterator<Bio>(sourceFile), std::istream_iterator<Bio>()};

    // Sort the guys by name
    std::sort(bio.begin(), bio.end(), [](const Bio& b1, const Bio& b2){ return b1.name < b2.name;});

    // Show output on screen
    std::copy(bio.begin(),bio.end(),std::ostream_iterator<Bio>(std::cout, "\n"));

    return 0;
}

Some comments. On StackOverflow, I cannot use files. So in my example program, I use a std::istringstream instead. But this is also an std::istream . You can use any other std::istream as well. So if you define an `````std::ifstream to read from a file, then it will work in the same way as the std::istringstream````.

And please see. The extractor operator does the whole work of reading the source File. It is encapsulated. No outside function needs to know, how it does.

In the main function, we define a std::vector and use its range contructor to specifiy where the data comes from. We give it the std::istream_iterator , which iterates over the input data and calls the extractor operator until verything is read.

Then we sort by names and copy the result to the output.

You may notice that fields in your input data are separted by space. This does in general not work for none atomic data. The name could exist of 2 parts and the address can have a street and a city. For this CSV (Comma separated Values) files have been invented.

Please see a more realistic soultion below.

#include <iostream>
#include <iterator>
#include <vector>
#include <algorithm>
#include <sstream>
#include <regex>

struct Bio
{
    // Data
    unsigned int id{}; 
    std::string name{};
    std::string address{};
    unsigned int age{};

    // Overload extractor operator to read all data
    friend std::istream& operator >> (std::istream& is, Bio& b) {
        std::string line{}; 
        std::regex re{";"};
        if (std::getline(is, line)) {
            std::vector<std::string> token{std::sregex_token_iterator(line.begin(), line.end(), re, -1), std::sregex_token_iterator()};
            if (4 == token.size()) {
                b.id = std::stoul(token[0]); 
                b.name = token[1]; 
                b.address = token[2];
                b.age = std::stoul(token[3]); 
            }
        }
        return is;
    }

    // Overload inserter operator to print the data 
    friend std::ostream& operator << (std::ostream& os, const Bio& b) {
        return os << b.id << ", " << b.name << ", " << b.address << ", " << b.age;
    }
};


std::istringstream sourceFile{R"(1; John Lenon; Street1 City1; 31
2; Paul McCartney; Street2 City2; 32
3; Ringo Starr; Street3 City3; 33
4; George Harrison; Address4; 34
)"};

int main()
{
    // Define Variable and read complete source file
    std::vector<Bio> bio{std::istream_iterator<Bio>(sourceFile), std::istream_iterator<Bio>()};

    // Sort the guys by name
    std::sort(bio.begin(), bio.end(), [](const Bio& b1, const Bio& b2){ return b1.name < b2.name;});

    // Show output on screen
    std::copy(bio.begin(),bio.end(),std::ostream_iterator<Bio>(std::cout, "\n"));

    return 0;
}

We have a new source format and main is unchanged. Just the extractor operator is modified. Here we are using a different iterator to get the source data.