Invalid initializer compiler-error at malloc of struct array

Question

I'm trying to read an arbitrary number of string items into an array of structs when my program initializes. I want to allocate heap memory for the

When the compiler gets to the following line, it throws an error: invalid initializer.

The first part of my code:

int main() { printf("Work starts in the vineyard.\n"); typedef struct { char* name[20]; unsigned int jobs; }Plantation; // read from list of plantations FILE *plantationFile = fopen("./data/plantations.txt", "r"); if (plantationFile==NULL) {perror("Error opening plantations.txt."); exit(1);} char line[20]; char *lp = line; int plantationCount; Plantation plantations[] = (Plantation *)malloc(sizeof(Plantation)); if (!feof(plantationFile)) { int i = 0; fgets(line, 20, plantationFile); scanf(lp, "%i", &plantationCount); realloc(plantations, sizeof(Plantation) * plantationCount); while( !feof(plantationFile) ) { fgets(line, 20, plantationFile); strcpy(*(plantations[i].name), lp); plantations[i].jobs = 1u; ++i; } } ...

What am I missing here?

The compiler output:

$ gcc -W -Wall vineyard.c vineyard.c: In function ‘main’: vineyard.c:30:32: error: invalid initializer Plantation plantations[] = (Plantation *)malloc(sizeof(Plantation)); ^

It also throws the same if I leave out typecasting.

$ gcc -W -Wall vineyard.c vineyard.c: In function ‘main’: vineyard.c:30:32: error: invalid initializer Plantation plantations[] = malloc(sizeof(Plantation)); ^~~~~~

Thanks!

dbush · Accepted Answer · 2020-04-29 20:53:22Z

You're defining plantations as an array, and you're trying to initialize an array with a pointer. An initializer for an array must be a brace enclosed list of initializers. More importantly, while arrays and pointers are related, they are not the same thing.

Define plantations as a pointer instead of an array:

Plantation *plantations = malloc(sizeof(Plantation));

Also, realloc can change where the allocated memory points to, so you need to assign the return value back:

plantations = realloc(plantations, sizeof(Plantation) * plantationCount);

You should also check the return value of malloc and realloc for errors.

Okay, I see what you mean. The malloc function's return type is pointer, and I'm trying to assign that to an array type variable. I guess I got confusedIf I keep plantations as a pointer, will I be able to use the plantations[i] syntax, or am I limited to pointer arithmetic? If so, is there a way I can use the [ ] syntax?
@Bundologus Yes, *(A + B) is exactly equivalent to A[B].

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