shoosh - Page 2 - Developer IT

cmd.exe: complex conditions?

- by shoosh

in DOS batch files, In an IF statement, is it possible to combine two or more conditions using AND or OR ? I was not able to find any documentation for that

C++: getting the address of the start of an std::vector ?

Sometimes it is useful to use the starting address of an std::vector and temporarily treat that address as the address of a regularly allocated buffer. For instance replace this: char* buf = new char[size]; fillTheBuffer(buf, size); useTheBuffer(buf, size); delete[] buf; With This: vector<char> buf(size); fillTheBuffer(&buf[0], size); useTheBuffer(&buf[0], size); The advantage of this is of course that the buffer is deallocated automatically and I don't have to worry about the delete[]. The problem I'm having with this is when size == 0. In that case the first version works ok. An empty buffer is "allocated" and the subsequent functions do nothing size they get size == 0. The second version however fails if size == 0 since calling buf[0] may rightly contain an assertion that 0 < size. So is there an alternative to the idiom &buf[0] that returns the address of the start of the vector even if the vector is empty? I've also considered using buf.begin() but according to the standard it isn't even guaranteed to return a pointer.

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C++ standard: dereferencing NULL pointer to get a reference?

- by shoosh

I'm wondering about what the C++ standard says about code like this: int* ptr = NULL; int& ref = *ptr; int* ptr2 = &ref; In practice the result is that ptr2 is NULL but I'm wondering, is this just an implementation detail or is this well defined in the standard? Under different circumstances a dereferencing of a NULL pointer should result in a crash but here I'm dereferencing it to get a reference which is implemented by the compiler as a pointer so there's really no actual dereferencing of NULL.

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C++: Life span of temporary arguments?

- by shoosh

When creating a new instance of a MyClass as an argument to a function like so: class MyClass { MyClass(int a); }; myFunction(MyClass(42)); does the standard make any grantees on the timing of the destructor? Specifically, can I assume that the it is going to be called before the next statement after the call to myFunction() ?

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Writing an ostream filter?

- by shoosh

I'd like to write a simple ostream which wraps an argument ostream and changes the stream in some way before passing it on to the argument stream. The transformation is something simple like changing a letter or erasing a word What would a simple class inheriting from ostream look like? What methods should I override?

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