Writing init function for C struct

Question

So this is my struct in a header file: ``` struct _Variable { char *variableName; char *arrayOfElements; int32_t address; }; typedef struct _Variable Variable; ``` and here is my implementation of the init function in .c file: ``` void initVariable(Variable *variable, char *variableName, char *arrayOfElements, int32_t address) { int lengthOfVariableNameWithTerminatingChar = strlen(variableName) + 1; variable->variableName = malloc( sizeof(char) * lengthOfVariableNameWithTerminatingChar); strncpy(variable->variableName, variableName, lengthOfVariableNameWithTerminatingChar); int lengthOfArrayOfElementsWithTerminatingChar = strlen(arrayOfElements) + 1; variable->arrayOfElements = malloc( sizeof(char) * lengthOfArrayOfElementsWithTerminatingChar); strncpy(variable->arrayOfElements, arrayOfElements, lengthOfArrayOfElementsWithTerminatingChar); variable->address = address; } ``` I get no errors when I compile but when I run my test file: ``` void test_initVariable() { printf("
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Accepted Answer

```
Variable *variable1;
```

gives you an uninitialised pointer. You don't own the memory it points to so can't safely write to it.

You need to allocate storage for `variable1`

```
Variable variable1;
initVariable(&variable1, "variable1", "1, 2, 3", 4);
```

would work.

If you want `variable1` to be dynamically allocated, it'd be easiest to have `initVariable` handle this

```
Variable* initVariable(char *variableName, char *arrayOfElements, int32_t address)
{
    Variable* var = malloc(sizeof(*var));
    if (var != NULL) {
        var->variableName = strdup(variableName);
        var->arrayOfElements = strdup(arrayOfElements);
        var->address = address;
    }
    return var;
}
```

Note that I've also simplified allocation/population of strings here. Your code works but if you're using a posix-compatible system, strdup is a much simpler way to achieve the same results.

As discussed in comments, you don't need to allocate storage if the string members of `Variable` will all be string literals. In this case, you could simplify things to

```
Variable* initVariable(char *variableName, char *arrayOfElements, int32_t address)
{
    Variable* var = malloc(sizeof(*var));
    if (var != NULL) {
        var->variableName = variableName;
        var->arrayOfElements = arrayOfElements;
        var->address = address;
    }
    return var;
}
```

Writing init function for C struct

Solution

Problem