Issues with malloc in C

Question

I seem to be having some issues with malloc in my code. Here's what's going on. I've got a struct created with a few values in it. From there, I'd like to make an array of structs. I think I've got the struct right, and some of the pointers, but I'm not sure.

Here's the struct:

typedef struct{ char name[25]; int courseID; } course;

From there, I try to initiate the new struct and malloc it at the same time by this:

course *courses = malloc(25*sizeof(course));

From here, I'm getting the error:

Invalid conversion from 'void*' to 'course*' [-fpermissive] course *courses = malloc(25*sizeof(course));

I don't really know what this means... I know I may be completely off course with this whole idea, so any help y'all can give would be great!

You're compiling as C++, not C. Change your compiler to gcc, or change the corresponding option in your IDE. — milleniumbug
– milleniumbug, Commented Feb 20, 2014 at 17:55

Zan Lynx · Accepted Answer · 2014-02-20 18:05:10Z

You must be using a C++ compiler. You want to compile with a C compiler.

Make sure your file name ends in .c not .cpp or .cc.

You also said you try to initialize (you said initiate but I am translating) the new struct. Malloc will not do that. Malloc allocated memory will contain random values left over from the last user of that memory. The calloc function might work better for what you want since it sets the memory to zero after allocating it.

I suspect "initiate" was ment to be "instantiate" not "initialise".

Soumen · Accepted Answer · 2014-02-20 18:57:07Z

You are initializing memory with malloc, which returns a void pointer to the allocated memory. You are then assigning this pointer to a course pointer. So there is a pointer mismatch and hence the warning. To bypass it use

course *courses = (course *)malloc(25 * sizeof(course))

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