Question

Since I’m very new to C programming, I have a probably very simple problem.

I got a struct looking like this

typedef struct Vector{
    int a;
    int b;
    int c;
}Vector;

Now I want to write an array of Vectors in a file. To achieve that, I thought to create following method scheme

String createVectorString(Vector vec){
    // (1)
}

String createVectorArrayString(Vector arr[]){
    int i;
    String arrayString;
    for(i=0; i<sizeof(arr); i++){
        //append createVectorString(arr[i]) to arrayString  (2)
    }
}

void writeInFile(Vector arr[]){
    FILE *file;
    file = fopen("sorted_vectors.txt", "a+");
    fprintf(file, "%s", createVectorArrayString(arr);
    fclose(file);
}

int main(void){

    // create here my array of Vectors (this has already been made and is not part of the question)
    // then call writeInFile

    return 0;
}

My main problems are at (1), which involves also (2) (since I have no clue how to work with Strings in C, eclipse is saying “Type “String” unknown”, although I included <string.h>)

So I read at some point that transforming an int to a String is possible with the method itoa().
As I understood it, I can simply do following

char buf[33];
int a = 5;
itoa(a, buf, 10)

However, I cannot bring that to work, let alone that I can’t figure out how to “paste” chars or ints into a String.

In my point (1), I would like to create a String of the Form (a,b,c), where as a, b and c are the “fields” of my struct Vector.

In point (2), I would like to create a single String of the Form (a1,b1,c1)\n(a2,b2,c2)\n...(an,bn,cn), whereby n is the amount of Vectors in the array.

Is there a quick solution? Do I confuse the concept of Strings from Java with them of C?

Answer 1

Yes, you do confuse the concept of strings in Java and C.

The C strings are rather inconvenient to work with. They require dynamic memory allocation, and what is worse, corresponding deallocation (which is possible but tedious). In your case, it might be best to remove strings completely, and implement whatever you need without strings.

To write a vector directly to file:

Vector vec;
FILE* file = ...;
fprintf(file, "%d %d %\n", vec.a, vec.b, vec.c);

To write an array of vectors, just do the above in a loop.