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I've tried to do a reference to a member variable, and understood that it does not work. Are there any way to do this? If not, is there a way to not constantly write "(* this)." ?
#include <iostream>
#include <string>
class Test
{
private:
std::string str_m;
void doSomething()
{
std::string& str = (*this).str_m; // does not work
std::cout << str << '\n';
}
public:
Test(std::string str): str_m(str)
{
(*this).doSomething();
}
};
int main()
{
Test test{"aaa"};
return 0;
}
VS compiler gave me: error C3867: 'Test::doSomething': non-standard syntax; use '&' to create a pointer to member
I've tried to do a reference to a member variable, and understood that it does not work. Are there any way to do this?
Yes:
struct Test {
std::string str_m;
void doSomething()
{
std::string& str = str_m;
}
};
[If not], is there a way to not constantly write "(* this)." ?
It is not clear from where you got the idea that you would have to write (*this).member. If you want to use this, then please write this->member, but there is no need to do this within the scope of the class (there are rare exceptions) and commonly it is frowned upon in favor of simply writing member.
PS: The error you report is from different code, not the one you posted.
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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 had a situation where I wanted to use a default paramenter for a reference in a VERY large legacy codebase for a fix.
static bool _defaultValue = false;
bool SomeFunction(const SomeComplexObject& iObj, bool& isSomeVal = _defaultValue )
{
// ... code
}
My issue is with using a static variable inside a namespace just dangling there by itself.
This code is going to be reviewed before being shipped but I'm unsure if it would be considered bad practice to have a dangling static variable like that.
Without the variable you can't have a default value for a reference. My options are very limited to make other changes to get the desired effect.
Would this be considered "hacky unprofessional coding"?
My suggestion would be:
Remove the global variable.
Don't use a default value for the reference argument.
Create a function overload that has only one argument.
Call the first function from the second function.
bool SomeFunction(const SomeComplexObject& iObj, bool& isSomeVal)
{
// ... code
}
bool SomeFunction(const SomeComplexObject& iObj)
{
bool dummy;
return SomeFunction(iObj, dummy);
}
Client code can call whichever function is appropriate in their context.
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I am reading a sample code that uses C++ and classes, I am new on C++ classes I can work with basics similar to this http://www.cplusplus.com/doc/tutorial/classes/, but I cant understand what the code below does mean or the color it is using visual studio c++
thanks
I am sorry if it is a fool question
It creates an object named some by instantiating the class some.
Then it calls the member function ToVector() on the object some and pass the result of the call to the function named function.
class is blue because it is a keyword of the C++ language.
The first some is green because it is the name of a class.
The second some is black because it is a variable.
And function and ToVector are red because the are functions.
Now this is ugly code because you "hide" the class some by reusing the same name for your variable. Also you do not need to put the word class here.
Here is a more complete and nicer version:
#include <vector>
class Some
{
public:
std::vector<int> ToVector()
{
return std::vector<int>(); //return an empty vector
}
};
int f(std::vector<int> v)
{
return 0;
}
int main(int, char**)
{
Some some; // Was "class some some"
return f(some.ToVector());
}
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Im trying to create a simple thread and have it execute.
My function definition is:
void MyClass::myFunction()
{
//Do Work
}
I'm creating the thread and executing it:
std::thread t1(myFunction);
Upon compiling my code, i get the following error:
error C3867: function call missing argument list; use '&MyClass::myfunction' to create a pointer to member.
Since my function does not take any parameters, i'm assuming i'm declaring it wrongly where i'm creating my thread? Any help will be appreciated, Thanks!!
If your method is a non-static member : You need an instance of your object to call the member function on.
If your method is static member, do what the compiler suggest : simply pass the address of your function.
Example:
class A
{
public:
void foo() { cout << "foo"; }
static void bar() { cout << "bar"; }
};
int main() {
std::thread t1(&A::foo, A()); // non static member
t1.join();
std::thread t2(&A::bar); // static member (the synthax suggested by the compiler)
t2.join();
return 0;
}
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These functions are both public members of a class. Private members of the class include *theCharArray and *theFloat.
This one works fine:
void theClass::getCharArray(char charArrayParam[]) const
{
strcpy(charArrayParam, this->theCharArray);
}
This one underlines "this" and VS express says "Error: Expression must be modifiable value"
void theClass::getFloat(float theFloatParam) const
{
theFloatParam = this->theFloat;
}
Please tell me what I'm doing wrong.
In theClass::getCharArray(char charArrayParam[]), charArrayParam is passed basically as a pointer to character array without any idea of the buffer size. This is kind of risky with the risk of overflowing the buffer. Netter interface would be:
theClass::getCharArray(char *charArrayParam, int charArraySize) const {
strncpy(charArrayParam, this->theCharArray, charArraySize - 1);
charArrayParam[charArraySize - 1] = 0;
}
And for the second one:
void theClass::getFloat(float *theFloatParam) const
{
*theFloatParam = this->theFloat;
}
otherwise, since theFloatParam being passed by value, changing that within the function has no effect on the caller.