Question

I have a piece of code that needs to be run from a restricted environment that doesn’t allow stdio (Flash’s Alchemy compiler). The code uses standard fopen/fread functions and I need to convert it to read from a char* array. Any ideas on how to best approach this? Does a wrapper exist or some library that would help?

Thanks!

EDIT: I should also mention that it’s reading in structs. Like this:

fread(&myStruct, 1, sizeof(myStruct), f);

Answer 1

I don’t know of any such wrapper, but I don’t think it would be too difficult to make your own. That’s because C’s approach to file I/O hides everything behind the FILE* interface, which actually makes it nicely object-oriented.

Since you’re using C rather than C++, I would suggest using preprocessor macros to replace every instance of fopen(), fclose() and fread() with MEM_fopen() etc. which are routines that you will define. You will need to define your own FILE type, for which you could simply use the following:

typedef unsigned char *FILE;

(If you need to manage EOF, you will instead need FILE to be a struct with an additional length field.)

Then your MEM_fread() function will look something like:

int MEM_fread(unsigned char *buf, size_t size, size_t n, FILE *f) {
    memcpy(buf, *f, size * n);
    *f += size * n;
    return n;
}

The signature for the MEM_fopen() “constructor” may need to change slightly, since the identifier you need is now a memory address instead of a filename.