Accessing struct via pointer in C and C++

Question

"Simple" question put short:

Why exactly does

JNIEnv *g_env = NULL;
(*g_env)->ExceptionDescribe(g_env);

compile in gcc (C)

but not in g++ (C++)

error: base operand of ‘->’ has non-pointer type ‘JNIEnv’ {aka ‘JNIEnv_’}

As I am working mainly with C++ I don't see why it should compile. As stated by the error, dereferencing the pointer will yield a "variable" and not a pointer anymore. I.e.: in C++ it would be either

g_env->ExceptionDescribe

or

(*g_env).ExceptionDescribe

as its not JNIEnv **

Answer 1

那是因为您的库代码不同。

在C中，JNIEnv是一个指针类型：

typedef const struct JNINativeInterface *JNIEnv;

在C ++中，JNIEnv是一个结构：

struct _JNIEnv;
typedef _JNIEnv JNIEnv;

因此，它当然会在一种情况下编译，而在另一种情况下不会编译。

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