malloc in structures

I was wondering if u could malloc in a structure parts at a t time.

Code:

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typedef struct {
    char part[10];
    char part2[20];
    randomstruct * ptr;
} struct1;

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Is there a way to malloc space for the part and part2 without touching the pointer for randomstuct
like
struct1 test;
test->part = malloc(sizeof(part));
???????

You would need to declare them as pointers.

Code:

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typedef struct {
    char* part;
    char* part2;
    randomstruct * ptr;
} struct1;

struct1 test;
test.part = malloc(10);
test.part2 = malloc(20);

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