c - 使用仅在运行时初始化的函数指针解析 [-Werror=maybe-uninitialized]

Question

我正在用 C11 编写一段代码，这应该会让我以后的程序生活更轻松。我有一个想要调用的通用 intersect 函数。然而，根据某些情况，intersect 函数实际上可能是一个不同的函数。

请注意，intersect 第三个参数的指针类型取决于 switch 情况，因此我无法真正概括它。

getnormal 也会出现相同的错误。

错误:

error: ‘intersect’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
   57 |   current_t = intersect(origin, direction, objects[i]);
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

代码:

float inline iPlane(vec3 origin, vec3 direction, plane * pla);
float inline iTriangle(vec3 origin, vec3 direction, triangle * tri);
float inline iSphere(vec3 origin, vec3 direction, sphere * sph);

vec3 inline nTriangle(triangle * obj, vec3 position);
vec3 inline nPlane(plane * obj, vec3 position);
vec3 inline nSphere(sphere * obj, vec3 position);


    float current_t;

    vec3 (*getnormal)();
    float (*intersect)();

    object * nearest_obj = NULL;
    for (int i = 0; i < object_count; ++i)
    {
        switch(objects[i]->shape){ // shape = enum{sphereobj, triangleobj, planeobj}
            case triangleobj:
                getnormal = &nTriangle; // real function that exists
                intersect = &iTriangle; // also a real function that exists
                break;
            case sphereobj:
                getnormal = &nSphere;
                intersect = &iSphere;
                break;
            case planeobj:
                getnormal = &nPlane;
                intersect = &iPlane;
                break;
        }

        current_t = intersect(origin, direction, objects[i]); // error here
    }

Answer 1

要消除警告，只需将函数指针变量初始化为 0 即可。

float (*intersect)() = NULL;

然后在使用它之前，检查它是否已初始化(以防万一所有枚举都没有包含在 switch 语句中，在这种情况下会引发另一个警告，但安全总比抱歉好)

assert (intersect);

或不带断言(可以通过某些编译器开关消除)

if (!intersect)
{
  // handle the error
}

如果这种情况可能发生:

if (intersect)
{
   current_t = intersect(origin, direction, objects[i]);
}
else
{
   current_t = 0.0; // some default value else you get the "uninitialized error" with current_t
}