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Can someone please point me to an explanation what e.g. QIODevice::WriteOnly actually does?
full line of code:
file.open(stderr, QIODevice::WriteOnly);
from that link
thanks
According to the documentation for the QIODevice class, WriteOnly is as enum constant with value 2. It indicates that the device is open for writing.
I believe that the following example for enum hack will be useful to you.
class MyClass1 {
public:
enum { SIZE=10 };
};
class MyClass2 {
public:
enum { SIZE=20 };
};
int main() {
cout << MyClass1::SIZE << "\t" << MyClass2::SIZE << endl;
}
QIODevice::WriteOnly is just a flag, you're saying that you want to open the file only for writing.
If you would want only to read the file, QIODevice::ReadOnly would be the necessary flag to use.
And to read and write use flag: QIODevice::ReadWrite:
file.open(stderr, QIODevice::ReadWrite);
Related
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I have about 40 questions. (all the answers to the questions are of either int or float data type)
I will display the question and ask the user to input his/her answer.
Then I will check if the answer is correct or not.
I need to implement this program in object oriented programming.
I thought about doing it this way,questions by questions..but is there another way of doing this? Please help me..
The code below is sort of a pseudocode . I use c++ .
class workout{
private:
float variables...;
public:
workout();
workout(float variables...);
void answers();
int Display();
~workout();
};
...
void workout::answers(){
declare variables;
display question1;
input answer1
check if correct
display question2;
input answer2
check if correct
display question3;
..and so on..
}
workout::~workout(){
}
int main(){
...
return 0;
}
Well you could have a Question class, and then go from there. Here's an example.
class Question
{
public:
std::string question
float answer;
Question(std::string _question, float _answer)
: question(_question), answer(_answer) {}
void Display() {}
bool Check(float input) {}
};
And then maybe create an array of questions?
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I'm writing a class that reads data from a file. The project is still in development, and it's likely that I'll change the file name or path later on, so I've stored it in a std::string for quicker editing.
Given that the file name is going to be used several times in a function, but is only going to be used in one function, is there a canonical cpp rule about where I should define the variable?
//don't know where I'll define this
std::string file_name = "path/to/file.foo";
//a.h file
class A {
public:
void fileFunc();
private:
//do i define it here?
};
//a.cpp file
A::fileFunc() {
//or do i define it here?
std::ifstream in(file_name);
if(in) {
//do things
}
else {
std::cerr << "couldn't open " << file_name;
}
}
Keeps all information close to thiers use.
It will help the readability and the performance. See: https://en.wikipedia.org/wiki/Locality_of_reference
So
A::fileFunc() {
const std::string file_name = "path/to/file.foo"; // pls use const when you can
...
or
A::fileFunc(const std::string& file_name) {
...
BTW, I think this should be on https://codereview.stackexchange.com/, not stackoverflow.
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I have a logging class with a std::stringstream member. I use it's output << overloading to get a nice easy means for catching all the data types std::stringstream gives me for free.
Here's the problem. After sending data into the stream, I want an easy way to flush it automatically to my destination (which is variable/dynamic in nature).
std::ostream will "auto flush" if you send an endl down it. That's and acceptable solution I would duplicate.
How can I implement that myself? Note that I don't want to override every operator<<() overload in std::stringstream!
I've done a similar thing. What I do is use an unnamed class instance to consume the output and put the flushing in the destructor. Something like this:
int i = 0;
MyClass() << "This is a log message containing an int: " << i;
// here, the class destructs and does whatever you need to do to flush the stream
Instead of subclassing std::stringstream, it's prefered to use composition (see Composition over inheritance).
With this, your class would look like this:
class Log{
std::stringstream _stream;
[...] // Constructor and other class logic
public:
Log& operator<<(string s){
_stream << s << endl;
return *this;
}
};
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Suppose there are two classes Class1 and Class2. given a condition I have to choose among them in shortest way possible without using if-else.
Means least lines of code.
At compile time only!!!
class class1{};
class class2{};
auto data = (((condition) ? class1 : class2) *)(variable)
Assuming you need to create object at compile time depending on a variable, you can try something like following
class class1{};
class class2{};
int main( int argc, char *argv[] )
{
constexpr bool variable =true;
/* x is object of type class1 or class2 depending on
compile time constant 'variable'
*/
typedef std::conditional<variable, class1, class2>::type x;
//std::cout << typeid(x).name() << '\n';
return 0;
}
See Here
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I know there is no specific rule of how to use or declare a string literal, like for example in my class, I want to use "MyName" string literal, and its the only class that will use it, for example,
// CFoo.h
class CFoo
{
public:
CFoo();
~CFoo();
void printString();
}
// CFoo.cpp
CFoo::CFoo()
{
}
CFoo::~CFoo()
{
}
void CFoo::printString()
{
std::cout << "MyName" << std::endl;
}
Now I want that "MyName" will have a descriptive name placeholder, like NameLiter or something like that. Should I use define preprocessor, or declare it as global in cpp as const std::string? Or should I make a private member variable and initialize it in the ctor initializer list?
Thanks!
Making it a private static const char* in CFoo would satisfy your requirements.