casting

问题 i asked a question here involving C++ and C# communicating. The problem got solved but led to a new problem. this returns a String (C#) return Marshal.PtrToStringAnsi(decryptsn(InpData)); this expects a TCHAR* (C++) lpAlpha2[0] = Company::Pins::Bank::Decryption::Decrypt::Decryption("123456"); i've googled how to solve this problem, but i am not sure why the String has a carrot(^) on it. Would it be best to change the return from String to something else that C++ would accept? or would i need

问题 I see some strange code in our project like follows.I test it and get the right answer.But I think it is illegal,Can anyone explain this to me? class Member { public: Member(): a(0),b(1) {} int a; int b; }; // contains `Member` as its first member class Container { public: Container(): c(0),d(0) {} Member getMemb(){return fooObject;} Member fooObject; int c; int d; }; and how we use it: int main() { auto ctain = new Container; auto meb = (Member *)ctain; // here! I think this is illegal cout

问题 I see some strange code in our project like follows.I test it and get the right answer.But I think it is illegal,Can anyone explain this to me? class Member { public: Member(): a(0),b(1) {} int a; int b; }; // contains `Member` as its first member class Container { public: Container(): c(0),d(0) {} Member getMemb(){return fooObject;} Member fooObject; int c; int d; }; and how we use it: int main() { auto ctain = new Container; auto meb = (Member *)ctain; // here! I think this is illegal cout

问题 I use jq to transform a complex json object into a tinier one. My query is: jq 'to_entries[]| {companyId: (.key), companyTitle: (.value.title), companyCode: (.value.booking_service_code)}' companies.json Now, the (.key) is parsed as a string, yet I want companyId to be a number. My result currently looks like this: { "companyId": "1337", "companyTitle": "Some company title", "companyCode": "oxo" } yet it should be like: { "companyId": 1337, "companyTitle": "Some company title", "companyCode":

问题 Let's say I have a Base class and several Derived classes. Is there any way to cast an object to one of the derived classes without the need to write something like this : string typename = typeid(*object).name(); if(typename == "Derived1") { Derived1 *d1 = static_cast&lt Derived1*&gt(object); } else if(typename == "Derived2") { Derived2 *d2 = static_cast &lt Derived2*&gt(object); } ... else { ... } 回答1: Don't. Read up on polymorphism. Almost every "dynamic cast" situation is an example of

问题 According to the responses in "Why subtract null pointer in offsetof()?" (and my reading of K&R), the C standard doesn't require that (size_t)((char *)0) == 0 . Still, I've never seen a situation where casting a null pointer to an integer type evaluates to anything else. If there is a compiler or scenario where (size_t)((char *)0) != 0 , what is it? 回答1: Well, as you know, the physical representation of null pointer of a given type is not necessarily all-zero bit pattern. When you forcefully

问题 I am trying to convert hex string of a very large number to a NUMERIC column CREATE OR REPLACE FUNCTION hex_to_int(hexval varchar) RETURNS NUMERIC AS $$ DECLARE result NUMERIC; BEGIN EXECUTE 'SELECT x''' || hexval || '''::NUMERIC(40,0)' INTO result; RETURN result; END; $$ LANGUAGE 'plpgsql' IMMUTABLE STRICT; There I am trying to do this: select hex_to_int(tx.value) from internal_transaction tx The error I get is : [42846] ERROR: cannot cast type bit to numeric Where: PL/pgSQL function hex_to

问题 Why when i use this: int a = 1; methodWithParamString(a + ""); a is cast to String, bu i can't use toString() on integer? int a = 1; methodWithParamString(a.toString()); Doesn't this: a+"" works like: a.toString() + "" ? 回答1: No, it works like String.valueOf( a ) + "" , which in turn behaves like new StringBuilder( String.valueOf( a ) ).append( "" ).toString() . The important thing to know is that it's all just done by the compiler, in other words it's syntactic sugar. This is why adding

问题 I have a problem where I have a pointer to an area in memory. I would like to use this pointer to create an integer array. Essentially this is what I have, a pointer to a memory address of size 100*300*2 = 60000 bytes unsigned char *ptr = 0x00000000; // fictional point in memory goes up to 0x0000EA60 What i would like to achieve is to examine this memory as an integer array of size 100*150 = 15000 ints = 60000 bytes, like this: unsigned int array[ 100 ][ 150 ]; I'm assuming it involves some

问题 I have a problem where I have a pointer to an area in memory. I would like to use this pointer to create an integer array. Essentially this is what I have, a pointer to a memory address of size 100*300*2 = 60000 bytes unsigned char *ptr = 0x00000000; // fictional point in memory goes up to 0x0000EA60 What i would like to achieve is to examine this memory as an integer array of size 100*150 = 15000 ints = 60000 bytes, like this: unsigned int array[ 100 ][ 150 ]; I'm assuming it involves some