CODEWITHSUNDEEP
cparsingcode-analysisc99static-code-analysis
rnunes
rnunes

Reputation: 2835

Detect struct fields access in C

I want to force that a certain struct never gets it's fields accessed directly, always using the struct functions.

Example:

struct NoOutsideAccess { int field1;}
struct example {NoOutsideAccess f1;}

NoOutsideAccess noa;
example * ex;

&noa          // OK
&ex->noa      // OK
noa.field1;   // ERROR
ex->f1.field1 // ERROR

I've looked at C parsers and analysis tools but I'm not sure that I can do this with them.

I don't want to change the struct since it's fields will be used directly within other modules. In this case I want some script that would point out where it's being used, so that the modules that aren't supposed to can change it.

But I did found a duplicate, not sure that will match every usage but will give it a shot.

Upvotes: 1

Views: 201

Answers (1)

wkz
wkz

Reputation: 2263

One way of create opaque objects in C is to hide the definition in a C-file and only export accessor prototypes along with a forward declaration of the object in the header file:

/* foo.h */

struct foo; /* forward declaration */

struct foo *foo_new (int bar, const char *baz);
void        foo_free(struct foo *foo);

int         foo_get_bar(struct foo *foo);
const char *foo_get_baz(struct foo *foo);

Then the implementation:

/* foo.c */

struct foo {
    int bar;
    const char *baz;
};

/* implementations of foo_{new,free,get_bar,get_baz} */

NOTE: Since outside code won't know the size of struct foo, you can only work with pointers to foos there (that's where foo_new comes in).

Upvotes: 5

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