CODEWITHSUNDEEP
c
user1998593
user1998593

Reputation:

Creating a function to read different data types

I am creating a C99 program and I'm needing some help to get out of a little redundancy of my code. I want to transform the following code into two calls of a function, but I don't know how to do it.

I want to read two files (each one has 15 entrances) and put their contents into two arrays. The problem is that these arrays are of a different data type.

Here is what I have:

typedef char string[30];

int
    _vInt[15];

string
    _vString[15];

FILE
    *_fInt,
    *_fString;

int main(){

      ...

      for(int i = 0; !feof(_fInt) && i < 15; ++i){
           fscanf(_fInt, "%d", &_vInt[i]);
           ...
      }

      for(int i = 0; !feof(_fString) && i < 15; ++i){
           fscanf(_fString, "%s", _vString[i]);
           ...
      }

      ...

 }

So, I don't want to use this for twice. I'd prefer to call a function twice instead:

readFile(_fInt, "%d", _vInt);
readFile(_fString, "%s", _vString);

The problem is that I don't know how the prototype of the function should be and neither how I should use it.

Yes, It's fine for me to use ugly void * solutions...

Upvotes: 3

Views: 143

Answers (4)

James
James

Reputation: 1371

Another solution would be to use enumerated type and table in your readFile() function.

#include <stdlib.h>
#include <stdio.h>

// Put in Header file
typedef char string[30];
typedef enum {
    ITInt    =  0,
    ITString =  1,
    ITMax
} InputTypes;

// Should be in module with readFile()
struct inputTypeEntry_s{
    const char *format;
    size_t sz;
};

struct inputTypeEntry_s inputTypeLUT[ITMax] = {
    { "%d", sizeof(int) },      // ITInt
    { "%s", sizeof(string) },   // ITString
};

int readFile(FILE *fp, InputTypes type, void *data) {
    char *ptr = (char *)data;
    for(int i = 0; !feof(fp) && i < 15; ++i){
        fscanf(fp, inputTypeLUT[type].format, ptr + (i * inputTypeLUT[type].sz) );
    }
    return 0;
}

Upvotes: 1

Carl Norum
Carl Norum

Reputation: 224944

Since you mentioned you can use C11 features, here's an example that uses C11 type-generic expressions. I used it to remove the requirement for passing the format string, too:

#include <stdio.h>

typedef char string[30];

#define generic_arg(X) _Generic(X, string: X, \
                                   default: &X)

#define generic_format(X) _Generic(X, string: "%s", \
                                      int:    "%d")

#define readFile(file, variable) for (int i = 0; i < 15; i++)            \
                                 {                                       \
                                     fscanf(file,                        \
                                            generic_format(variable[i]), \
                                            generic_arg(variable[i]));   \
                                 }

int main(void)
{
    int _vInt[15];
    string _vString[15];

    FILE *_fInt = fopen("ints", "r");
    FILE *_fString = fopen("strings", "r");

    readFile(_fInt, _vInt);
    readFile(_fString, _vString);

    for (int i = 0; i < 15; i++)
    {
        printf("%d %s\n", _vInt[i], _vString[i]);
    }

    fclose(_fInt);
    fclose(_fString);

    return 0;
}

I'm not sure if this is a really great example - it's certainly more complicated than your two-for-loop solution, but I think it meets your requirements.

Upvotes: 0

utopianheaven
utopianheaven

Reputation: 1277

You can extract out the type to a (void *), but it's not going to be pretty.

void foo(FILE *file, const char *format, void *arr, size_t size) {
  for(int i = 0; !feof(file) && i < 15; ++i){
       fscanf(file, format, ((char *)arr) + (size * i));
       ...
  }      
}

The function call would look like

foo(_fInt, "%d", (void *)&_vInt, sizeof(int))

Upvotes: 0

tom
tom

Reputation: 19153

You can use a macro.

#define readFile(file, fmt, arr) \
    for (int i = 0; !feof(file) && i < 15; ++i) { \
        fscanf(file, fmt, arr[i]); \
    }

readFile(_fInt, "%d", &_vInt);
readFile(_fString, "%s", _vString);

Upvotes: 1

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