如何将结构作为参数传递

Question

I am writing a piece of C code, and I am supposed to use a static library, containing one function. I have a header file, containing a typedef struct, which I am supposed to use as input argument.

My understanding of the function is, that I create a structure of the data type defined in header file and give it as pointer to the function and the function will fill the structure. The other two arguments are data and strlen(data) .

My question is. How do I create the structure in my .c file and how do I get the data from it?

Here is a my .h file

#include <stdint.h>
#include <stddef.h>
typedef struct
{
  uint8_t arrayA[2];
  uint8_t arrayB[16];
} structDefinition;

void getData(structDefinition* myStructure, void const* data, size_t dataSize);

And this is my .c file

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include "myHeader.h"

structDefinition myStructure;

int main()
{
    char data[5] = {'123AF'};
    size_t dataSize = 5;

    getData(*myStructure, *data, dataSize);
    printf(mySignature.arrayA);
    printf(mySignature.arrayB);
    return 0;
}

Answer 1

You need to pass the address of the structure for your function.

myStructure is a object of type struct Definition

Now pass

getData(&myStructure,data,dataSize);

data is an array of type char and it can be passed to a char *

Please check character array initialization

char data[6] = "123AF";/* char array comes with a nul terminator */

and length of the char array can be got from

size_t dataSize = strlen(data);

If you want to know the strlen() then 3rd parameter is not required. Because you can get it from the string passed.

Answer 2

This definition

char data[5] = {'123AF'};

is wrong. '123AF' is a character literal.. Its value is implementation defined. It seems you mean

char data[5] = { "123AF" };

where "123AF" is a string literal.

The function call

getData(*myStructure, *data, dataSize);

is also wrong. It must look like

getData( &myStructure, data, dataSize );

These output statements can be also wrong because it seems the arrays can contain characters without terminating zeroes

printf(mySignature.arrayA);
printf(mySignature.arrayB);

To output correctly these arrays you need to look through the definition of the function getData to determine how the arrays are assigned.