CODEWITHSUNDEEP
c++casting
user3007875
user3007875

Reputation: 153

Casting works differently in 2 cases

I have a class EDSobject:

class EDSobject
{
public:
    ...

    int index;
    int subindex;
    std::string parameter;
    std::string dataType;
    int value;
};

In my code I write objects of this class to stringstream file:

if (obj.dataType == "0x0002" || obj.dataType == "0x0003" || obj.dataType 
== "0x0004") //signed data types
                {
                    file << "    0x" << obj.subindex << " " << 
obj.parameter << " = " << dec << (int16_t)obj.value << endl;
                }
                else //unsigned data types
                {
                    file << "    0x" << obj.subindex << " " << 
obj.parameter << " = " << dec << obj.value << endl;
                }

You can see that if dataType is "2", "3" or "4", I cast value to signed integer (values inside obj.value are unsigned integer). This works ok. For instance, I get -1386 from 64150.

The problem is when I tried to do it with only casting, like so:

void EDScastAllValues()
{
for (EDSobject obj : EDScontainer)
{
    if (obj.dataType == "0x0002" || obj.dataType == "0x0003" || 
obj.dataType == "0x0004") //signed data types
    {
        int16_t newVal = static_cast<int16_t>(obj.value);
        //or int16_t newVal = (int16_t)obj.value;
        obj.value = newVal;
    }
}
}

And then writing all objects the same, without if statement.

file << "    0x" << obj.subindex << " " << obj.parameter << " = " << dec << obj.value << endl;

Here, the obj.value doesn't change - 64150 is still 64150. I don't get negative values like before.

What am I doing wrong here?

EDIT: forgot to add definition of EDSContainer.

set<EDSobject, cmp> EDScontainer;

Upvotes: 0

Views: 85

Answers (1)

Nick H
Nick H

Reputation: 154

You are copying objects out of your container and modifying the copies. You want: 

for(auto& obj: EDSContainer)

Upvotes: 1

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