Problem with structs in c

Question

Hi guys i've got a problem here with structs, the thing is, i've created a struct and then created a function that captures the employee details referenced from that struct. Now the problem comes when i try to call the function in the main. please give me some pointers as to how to call the function. the code is as follows:

typedef struct employeeType
{
    char name;
    int employeeNumber;
    float salary;
    float taxPercentage;
}EMPLOYEE;

void enterDetails(EMPLOYEE details)
{  
    FILE *file;
    file = fopen("employees.txt","w");
    if(file == NULL)
    {
        printf("File error!!!");
        exit(0);
    }
    else
    {
        fprintf(file,"%s",details);
    }
    fclose(file);

}

void main()
{ 
  enterDetails();
}

I don't know what parameters to pass to the function in the main

Answer 1

I've annotated your code with some other issues to consider

typedef struct employeeType
{
     /* THIS IS ONLY ONE CHARACTER... SEEMS WRONG */
     /* should be 'char name[someMaxSize]', or 'char *name' */
    char name;  
    int employeeNumber;
    float salary;
    float taxPercentage;
}EMPLOYEE;

/* As pointed out by 'Cody Gray', this function is called 'enterDetails'
 * does it really need to have a parameter at all, or should it be responsible
 * for taking the details from the user?  Is it an appropriately 
 * named method for the task it's actually performing 
 * (would saveDetails be better for example)?
 */
void enterDetails(EMPLOYEE details)
{  
    FILE *file;
    file = fopen("employees.txt","w");
    if(file == NULL)
    {
        printf("File error!!!");
        exit(0);
    }
    else
    {
        /* THIS IS PASSING A STRUCTURE AS A STRING */
              /* You probably want to write out the individual fields instead */
              /* fprintf(file, "%s,%d", details.name, details.employeeNumber); etc */
        fprintf(file,"%s",details);  
    }
    fclose(file);

}

void main()
{ 
  EMPLOYEE details;   
  /* populate details somehow then pass it in to the function*/ 
  enterDetails(details);
}

You may also want to consider passing details into the function as a pointer, although that would change your function signature, it would mean that you're not pushing as much information onto the stack.

If you go with the pointer version then:

void enterDetails(EMPLOYEE details) 

would become

void enterDetails(EMPLOYEE *details) 

and the main would become:

void main()
{ 
  EMPLOYEE details;   
  /* populate details somehow then pass it in to the function as pointer */ 
  enterDetails(&details);
}

You would also need to change the way you use details within your function, but as I've already said, I believe your fprintf call is broken already.

Answer 2

void main()
{ 
  EMPLOYEE details;
   // get the value of element of struct from scanf or from other way
   printf("Enter Name : ");
   scanf("%s", details.name);  // same for others, change the format specifier according to their data type
  enterDetails(details);
}

And struct should be like

typedef struct employeeType
{
    char name[];  // should be an array or pointer, to store name
    int employeeNumber;
    float salary;
    float taxPercentage;
}EMPLOYEE;

Answer 3

You can pass the pointer of the struct

void main()
{
    EMPLOYEE employee;
    .....
    enterDetails(&employee);
}

void enterDetails(EMPLOYEE *details)
{

}

Answer 4

You need to pass a reference, not a value... If you pass EMPLOYEE value as in the previous post, it will be copied, the copy will be modified, not the original

 void enterDetails(EMPLOYEE* emp) {
    // do stuffs
 }

 void main() {
   EMPLOYEE emp;
   enterDetails(&emp);
 }

Answer 5

The first problem is that your structure isn't correct. You can't store the employee's name on the name field since it's only one byte. You have to make it an array (it's simpler on this case) or a pointer to allocated memory.

If you want to make it an array, then you should define the maximum size of the array. In our example we will just make it 100 bytes, it will be more than enough to store any name.

#define MAX_NAME 100

typedef struct employeeType
{
    char name[MAX_NAME];
    int employeeNumber;
    float salary;
    float taxPercentage;
}EMPLOYEE;

Second, you're function naming is confusing. enterDetails should just populate the structure you passed. Third, your enter Details should accept a pointer to the EMPLOYEE structure. If you want to pass any value to a function that's going to change it's content, then you can only do that using pointers (or references if you're using C++ but that's basically a pointer). So enterDetails should be,

void enterDetails(EMPLOYEE *details)
{
    printf("\nEnter the employee's name ");
    scanf("%s", details->name); // this isn't secure since it doesn't perform bound checking.

    printf("\nEnter employee number ");
    scanf("%d", &details->employeeNumber);

    printf("\nEnter employee salary ");
    scanf("%f", &details->salary);

    printf("\nEnter tax percentage ");
    scanf("%f", &details->taxPercentage);

}

And finally, if you want to store the contents of the structure to a file that you want humans to read, then you should format the contents of the structure and dump it onto a file.

int writeToFile(EMPLOYEE *details) /* accepting the structure will work as well but it's faster and efficient to pass the structure's pointer */    
{
    FILE *file;

    file = fopen("employees.txt","w");
    if(file == NULL) {
       printf("File error!!!");
       return 0;
    }

    fprintf(file, "\nEmployee Name: %s", details->name);
    fprintf(file, "\nEmployee Number: %d", details->employeeNumber);
    fprintf(file, "\nSalary: %f", details->salary);
    fprintf(file, "\nTax Percentage: %f", details->taxPercentage);

    fclose(file)
    return 1;
}

And main

int main(void)
{
    EMPLOYEE details;

    enterDetails(&details); // passing the pointer here is a must
    if (!writeToFile(&details)) { // passing the pointer since it's faster
       printf("\nError writing to file");
       return 1;
    } else {
       printf("\nSuccess!");
       return 0;
    }
}

And in your case, you don't need to pass any parameters to main. But if you want to know how to pass parameters, then here is a quick example.

int main(int argc, char **argv)
{
    int i;

    for (i = 0; i < argc; i++)
        printf("\n%s", argv[i]);

    return 0;
}