# Extra Clang Tools 18.1.8 documentation

## clang-tidy - bugprone-suspicious-realloc-usage

# bugprone-suspicious-realloc-usage

This check finds usages of `realloc` where the return value is assigned to the same expression as passed to the first argument: `p = realloc(p, size);` The problem with this construct is that if `realloc` fails it returns a null pointer but does not deallocate the original memory. If no other variable is pointing to it, the original memory block is not available any more for the program to use or free. In either case `p = realloc(p, size);` indicates bad coding style and can be replaced by `q = realloc(p, size);`.

The pointer expression (used at `realloc`) can be a variable or a field member of a data structure, but can not contain function calls or unresolved types.

In obvious cases when the pointer used at realloc is assigned to another variable before the `realloc` call, no warning is emitted. This happens only if a simple expression in form of `q = p` or `void *q = p` is found in the same function where `p = realloc(p, ...)` is found. The assignment has to be before the call to realloc (but otherwise at any place) in the same function. This suppression works only if `p` is a single variable.

Examples:

    struct A {
      void *p;
    };

    A &getA();

    void foo(void *p, A *a, int new_size) {
      p = realloc(p, new_size); // warning: 'p' may be set to null if 'realloc' fails, which may result in a leak of the original buffer
      a->p = realloc(a->p, new_size); // warning: 'a->p' may be set to null if 'realloc' fails, which may result in a leak of the original buffer
      getA().p = realloc(getA().p, new_size); // no warning
    }

    void foo1(void *p, int new_size) {
      void *p1 = p;
      p = realloc(p, new_size); // no warning
    }