C++ initialize variable based on condition [closed]

Answer 1

You can use the ternary or conditional operator. The basic form is:

condition ? valueIfTrue : valueIfFalse

Example:

const char* x = (SomeFunction() == 0) ? "is null" : "is not null";

When SomeFunction() returns 0, x is initialised with "is null", otherwise with "is not null".

Answer 2

What you want to achieve is not possible. The only thing you can do, is to initialize them with a ternary as suggested or move the initialization into a if block and leave the declaration out.

Answer 3

You say you are modifying an existing old project. In that case it makes sense to keep changes minimal.

However, you can't define the size of a static array at run time. If you want, you can keep the array as it currently is and make sure you don't use the 4th element when data->nDataVar() != 1.

Then:

const size_t dataSize = data->primType().getTypeSize() * dimsOut[0] * dimsOut[1] * dimsOut[2] * (data->nDataVar() != 1 ? 1 : dimsOut[3]);

It's worth mentioning the dimsOut array seems completely unnecessary to calculate the value of dataSize, but who knows what else your code is doing with it. If it is only used inside a single function/method then you could easily replace it with something else, such as std::vector.

Answer 4

Your question is a bit confusing, or rather not enough information was provided. It is not clear if the dimsOut[] variable is needed elsewhere. In case it is used ONLY for the computation of dataSize, you can use directly the dims[] array and do:

int typeSize = data->primType().getTypeSize() * data->nDataVar();
int dimension = dims[0] * dims[1] * ((condition) ? dims[2] : 1);
const size_t dataSize = typeSize * dimension;

In case that dimsOut is used elsewhere, then you can use the first block modifying the dimsOut[3] assignment with the ternary operator:

int dimsOut[4];
dimsOut[0] = data->nDataVar();
dimsOut[1] = dims[0];
dimsOut[2] = dims[1];
dimsOut[3] = (condition) ? dims[2] : 1;

const size_t dataSize = data->primType().getTypeSize() * dimsOut[0] * dimsOut[1] * dimsOut[2] * dimsOut[3];