Passing Structs Into An Array Of Structs.

This is a discussion on Passing Structs Into An Array Of Structs. within the C Programming forums, part of the General Programming Boards category; Here I have a C program that is supposed to pass structs that it reads from a .csv file to ...

  1. #1
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    Passing Structs Into An Array Of Structs.

    Here I have a C program that is supposed to pass structs that it reads from a .csv file to get the fields for the individual structs. Then it should pass the filled struct into the array. But it's not putting the information in the right slots in the array. I'm pretty new to C. I generally work with C#. So I'm not used to pointers and addresses and the like. I might have done something wrong there. If someone can point me in the right direction that would be great!

    Thanks!

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <fcntl.h>
    #include <string.h>
    
    
    typedef struct {
        //COUNTRY ID, COUNTRY NAME, POPULATION, LIFE EXPECTANCY, AND DATE OF FOUNDING
        char *id;
        char *name;
        int population;
        float lifeExpectancy;
        int year;
    }CountryData;
    CountryData FormatData(char *data);
    int main()
    {
        int         fr                      =   open("SampleCountriesInput.csv", O_RDONLY);
        int         inputSize               =   200;
        int         i                       =   0;
        int         j                       =   0;
        char        line[inputSize];
        char        buff[1];
        ssize_t     n;
        CountryData countries[50];
        CountryData country;
        do
        {
            n = read(fr,buff,1);
            if(buff[0] == '\n')
            {
                country = FormatData(line);
                //countries[j] = FormatData(line);
                strncpy(&countries[j].id, &country.id,3);
                strncpy(&countries[j].name, &country.name, 18);
                countries[j].population = country.population;
                countries[j].year = country.year;
                countries[j].lifeExpectancy = country.lifeExpectancy;
                j++;
                i=0;
            }
            else
                line[i] = buff[0];
            i++;
        }while( n != 0);
        j--;
        while(j!=0)
        {
            printf(countries[j].name);
            j--;
        }
        return 0;
    }
    
    CountryData FormatData(char *data)
    {
        CountryData country;
        char *token[20];
        int j, i = 0;
        token[0] = strtok(data, ",");
        while(token[i] != NULL)
        {
            i++;
            token[i] = strtok(NULL, ",");
        }
        country.id = token[1];
        country.name = token[2];
        country.lifeExpectancy = atof(token[8]);
        country.population = atoi(token[7]);
        country.year = atoi(token[6]);
        return country;
    }

  2. #2
    and the hat of wrongness Salem's Avatar
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    strncpy(&countries[j].id, &country.id,3);
    strncpy(&countries[j].name, &country.name, 18);
    The problem here is that your countries[].id (and name) are just pointers, and have not been allocated any space.


    country.id = token[1];
    country.name = token[2];
    This "works" because you´re setting a pointer to somewhere in your input string (data).


    Start with char id[4] (for example), and use strcpy() to copy the data from one place to another.

    I see you use strncpy(), which is good at limiting the data, but it does NOT guarantee the result is a proper C string (with a /0 at the end).

    If all your data at the moment is a valid length, then get something working with strcpy() first.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
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    Code:
    // hard way
           if(buff[0] == '\n')
            {
                country = FormatData(line);
                //countries[j] = FormatData(line);
                strncpy(&countries[j].id, &country.id,3);
                strncpy(&countries[j].name, &country.name, 18);
                countries[j].population = country.population;
                countries[j].year = country.year;
                countries[j].lifeExpectancy = country.lifeExpectancy;
                j++;
                i=0;
            }
    Code:
      // easy way
           memcpy(&countries[j],&country,sizeof(countrydata));

  4. #4
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    Or better still:
    Code:
    countries[j] = country

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