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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 don’t know how to implement reading data and put it into the structure
There is a config.txt file, it stores data like
someBigText=ASDSDdasdsa (can be more +1000 simbol)
isOkay=true
myAge=24
struct Config {
std::string Name;
std::string StringValue;
};
assuming your config is splitted in sections like:
[myImportantSection]
someBigText = "foo tha can be more +1000 simbols"
isOkay = true
myAge = 24
and assuming you are using boost:
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/ini_parser.hpp>
boost::property_tree::ptree myPtree;
boost::property_tree::ini_parser::read_ini("config.txt", myPtree);
auto text{myPtree.get<std::string>("myImportantSection.someBigText")};
auto isOk{myPtree.get<bool>("myImportantSection.isOkay")};
auto age{myPtree.get<int>("myImportantSection.myAge")};
struct Config
{
std::string text{};
bool ok{false};
int age{0};
};
Config myConfig;
myConfig.text = text;
myConfig.ok = isOk;
myConfig.age = age;
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I have the object listed below.
class Customer
{
private:
std::string customerName;
std::string customerLastName;
std::string customerIdentityNumber;
std::vector<std::unique_ptr<Account>> customerAccounts;
}
How would one go about serializing this object? I've tried finding examples but these are all using some complex libraries. Surely there must be an easier way?
Coming from Java this is new to me.
I really recommend a serialization library such as boost::serialization
Its a great library, easy to use, extremely fast, and has much more than just this!
It's exactly what you're looking for.
I prefer a very simple and basic implementation. Lets assume that Serialize() function has already been implemented for Account class.
The implementation of Serialize() function of Customer class can be:
void Customer::Serialize(Archive& stream)
{
if(stream.isStoring()) //write to file
{
stream << customerName;
stream << customerLastName;
stream << customerIdentityNumber;
stream << customerAccounts.size(); //Serialize the count of objects
//Iterate through all objects and serialize those
std::vector<std::unique_ptr<Account>>::iterator iterAccounts, endAccounts;
endAccounts = customerAccounts.end() ;
for(iterAccounts = customerAccounts.begin() ; iterAccounts!= endAccounts; ++iterAccounts)
{
(*iterAccounts)->Serialzie(stream);
}
}
else //Reading from file
{
stream >> customerName;
stream >> customerLastName;
stream >> customerIdentityNumber;
int nNumberOfAccounts = 0;
stream >> nNumberOfAccounts;
customerAccounts.empty(); //Empty the list
for(int i=0; i<nNumberOfAccounts; i++)
{
Account* pAccount = new Account();
pAccount->Serialize(stream);
//Add to vector
customerAccounts.push_back(pAccount);
}
}
}
The code is self-explanatory. But idea is to archive count and then every element. This help while deserializing from file.
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Hi I dnt have any knowledge on Multithreading or Parallel programing.
I need to load multiple file for an application, in which the load time does not affect the application or response to user.
I used CreateThread with that I cannot able to load data to a class variable.
Any guidance of how to do this in VC++ will be a great help.
Thanks in Advance !!
For example,
My application is streaming content meantime I need to load a big image to to class variable (Bitmap), which should not affect the streaming i.e without pause.
Modern C++ allows you to use hi level abstract features such as std::future:
struct Data {
// file name just for info
std::string file_name;
// here is data from file ...
static Data load(const std::string& name) {
Data data{ name };
// todo load from file
return std::move(data);
}
};
std::vector<std::string> names = { "file1.txt", "file2.txt", "file3.txt" };
std::vector<std::future<Data>> results;
for (const auto& name : names) {
// load from the name file asynchronously
auto future = std::async(std::launch::async, &Data::load, std::ref(name));
results.emplace_back(future);
}
// gather result
for (auto& future : results) {
Data& data = future.get();
// todo use data from the file object
}
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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);
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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.