back again with a "using C in C++" kind of question. In my experiment to use APR in C++ I am facing a new issue. The C++ header file:
#ifndef TEST_STRINGCOMMONS_H_
#define TEST_STRINGCOMMONS_H_
namespace test {
class StringCommons {
public:
static char* substr_offset_length(apr_pool_t *pool, const char* input,
apr_size_t offset, apr_size_t length);
};
} /* namespace test */
#endif /* TEST_STRINGCOMMONS_H_ */
and the C++ implementation of it:
namespace test {
...
char* substr_offset_length(apr_pool_t *pool, const char* input, apr_size_t offset, apr_size_t length)
{
apr_size_t *input_length = apr_pcalloc(pool, sizeof(apr_size_t));
...
}
} // namespace test
By compiling this class I get the error:
error: invalid conversion from ‘void*’ to ‘test::apr_size_t* {aka long unsigned int*}’ [-fpermissive]
I would like to know what is wrong with this code. Somebody help me please.
Best regards, SK
apr_pcalloc返回一个void *,您可能需要将其static_cast到所需的类型(在这种情况下为apt_size_t *)。
In C++, any pointer can be implicitly converted to void*
(just as in C). But unlike C, in C++ a pointer of void*
type can't be implicitly converted to int*
, or void**
, or std::string*
, or whatever.
The solution is reinterpret_cast
:
apr_size_t *input_length = reinterpret_cast<apr_size_t *>(apr_pcalloc(pool, sizeof(apr_size_t)));
Although why would anybody want to allocate a lonely long
on the heap is beyond me.
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