I have to call one simple functions with different datatypes in c++. eg,
void Test(enum value)
{
int x;
float y; // etc
if(value == INT)
{
// do some operation on x
}
else if(value == float)
{
// do SAME operation on y
}
else if(value == short)
{
// AGAIN SAME operation on short variable
}
.
.
.
}
Thus I want to eliminate the repetitive code for different datatypes ...
So , I tried to use macro ,depending on values of enum, to define same variable for different datatypes .. but then not able to differentiate between the MACROS
e.g.
void Test(enum value)
{
#if INT
typedef int datatype;
#elif FLOAT
typedef float datatype;
.
.
.
#endif
datatype x;
// Do operation on same variable
}
But now every time the first condition #if INT is getting true.
I tried to set different values of macro to differentiate but not working :(
Can anyone help me achieve the above thing.
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
//type generic method definition using templates
template <typename T>
void display(T arr[], int size) {
cout << "inside display " << endl;
for (int i= 0; i < size; i++) {
cout << arr[i] << " ";
}
cout << endl;
}
int main() {
int a[10];
string s[10];
double d[10];
for (int i = 0; i < 10; i++) {
a[i] = i;
d[i] = i + 0.1;
stringstream std;
std << "string - "<< i;
s[i] = std.str();
}
display(a, 10); //calling for integer array
display(s, 10); // calling for string array
display(d, 10); // calling for double array
return 0;
}
If you really want your function to be generic, template is the way to go. Above is the way to do and call the method from main method. This might be of some help for you to reuse a function for different types. Pick up any tutorial or C++ books for complete understanding on templates and get a grip of the full concepts. Cheers.
You can use templates to achieve you purpose.
Simply write a template function which take the value in the function argument which is of generic type and put the operational logic inside it. Now call the function with different data types.
I advice you to use function overloading:
void foo(int arg) { /* ... */ }
void foo(long arg) { /* ... */ }
void foo(float arg) { /* ... */ }
Supposing you want do the same operation with integer and long types you can eliminate the code repetition in this way:
void foo(long arg) { /* ... */ }
void foo(int arg) { foo((long) arg); }
Related
My code is below. This works, It allows me to have exactly one range in my lambda.
So I guess what my question is, is how do I achieve the same results without using
"if(LOOP > 2 && LOOP < 5){int THERANGEVALUE = 2; FUNC[THERANGEVALUE]();}"?
And instead initialize an item in my captureless lambda as being ranged instead. aka, item_2 being item_range(2,4). And then also being able to continue my lambda normally, whereas Item_3 will equate to item_5.
Thank you for any help in advance, I will gladly add more input if requested.
#include <iostream>
using namespace std;
void (*FUNC[3])(void) = { //captureless lambda.
/*ITEM_0*/[](){ cout << "x" << endl;},
/*ITEM_1*/[](){cout << "y" << endl;},
/*ITEM_2->ITEM_4*/[](){cout<<"z";}
};
/*Here the [](){code;} lambda is acting as a stand-in for void FUNC() so it shouldn't touch anything outside of its scope*/
int LOOP = 4;
int main()
{
if(LOOP > 2 && LOOP < 5){int THERANGEVALUE = 2; FUNC[THERANGEVALUE]();}
FUNC[LOOP]();
return 0;
}
Adding on to this, below is the solution I came up with after asking a friend. To my surprise it was actually a lot simpler than I expected. While I couldn't initialize each item in the lambda in a range easily, I could pass it into an array and set a range inside of the array instead. So while it's not quite what I was looking for, it's...good enough for my purposes. Thanks Jaime if you see this. Otherwise I'd use PilouPili's answer below.
#include <iostream>
using namespace std;
void (*FUNC[4])(void) = { //captureless lambda.
/*ITEM_0*/ [](){ cout << "x" << endl;},
/*ITEM_1*/ [](){cout << "y" << endl;},
/*ITEM_2->ITEM_4*/[](){cout<<"z";},
/*ITEM_5*/ [](){cout<<"z";}
};
int LOOP = 4;
int main()
{
int ARR[5]={};
for(int I = 0; I < 6;I=I+1){//handling of ranged values.
if(I>2 && I<5){ARR[I]=2;} else {ARR[I]=I;}
}
FUNC[ARR[LOOP]]();
return 0;
}
I only see to way :
either extend your function array -> That's FUNC1 in the next example
change the value given in operator [] -> That's FUNC2 in the next example
#include <iostream>
#include <vector>
using namespace std;
std::vector<void (*)(void)> init_FUNC()
{
std::vector<void (*)(void)> func(5, [](){cout<<"z";});
func[0]=[](){ cout << "x" << endl;};
func[1]=[](){ cout << "y" << endl;};
return func;
}
std::vector<void (*)(void)> FUNC1= init_FUNC();
class FUNC_MAP
{
void (*_FUNC[3])(void) = { //captureless lambda.
/*ITEM_0*/[](){ cout << "x" << endl;},
/*ITEM_1*/[](){cout << "y" << endl;},
/*ITEM_2->ITEM_4*/[](){cout<<"z";}
};
typedef void (*FUNC_MAP_OUT)(void);
public:
FUNC_MAP_OUT operator[](int i)
{
if(i>2 && i<5)
{return _FUNC[2];}
else
{return _FUNC[i];}
}
};
FUNC_MAP FUNC2;
/*Here the [](){code;} lambda is acting as a stand-in for void FUNC() so it shouldn't touch anything outside of its scope*/
int LOOP = 1;
int main()
{
FUNC1[LOOP]();
FUNC2[LOOP]();
return 0;
}
So I am new to c++, coming from C#. This is giving me several errors when compiling, which all seem to relate to this object declaration. Anyone able to show me the right way to do this?
I get an undeclared identifier where i declare tri(sideLength).
I have used this as a reference for object declaration, but it doesn't seem to be helping me.
Thanks.
#include <iostream> // Provides cout
#include <iomanip> // Provides setw function for setting output width
#include <cstdlib> // Provides EXIT_SUCCESS
#include <cassert> // Provides assert function
#include <stdexcept>
#include <math.h>
using namespace std; // Allows all standard library items to be used
void setup_cout_fractions(int fraction_digits)
// Precondition: fraction_digits is not negative.
// Postcondition: All double or float numbers printed to cout will now be
// rounded to the specified digits on the right of the decimal.
{
assert(fraction_digits > 0);
cout.precision(fraction_digits);
cout.setf(ios::fixed, ios::floatfield);
if (fraction_digits == 0)
cout.unsetf(ios::showpoint);
else
cout.setf(ios::showpoint);
}
int main()
{
const int MAX_SIDE_LENGTH = 6;
const int INITIAL_LENGTH = 1;
const int DIGITS = 4;
const int ARRAY_SIZE = 6;
// Set up the output for fractions and print the table headings.
setup_cout_fractions(DIGITS);
// Each iteration of the loop prints one line of the table.
for (int sideLength = 0; sideLength < MAX_SIDE_LENGTH; sideLength += 1)
{
EquilateralTriangle tri(sideLength);
//Square sq(sideLength);
//Pentagon_Reg pent(sideLength);
//Hexagon_Reg hex(sideLength);
//Heptagon_Reg hept(sideLength);
//Octagon_Reg octa(sideLength);
cout << "Type: " << tri.Name() << "has area: " << tri.Area() << " with SideLength = " << sideLength;
}
return EXIT_SUCCESS;
}
//Template
class GeometricFigure
{
public:
GeometricFigure() { }
double SideLength;
virtual double Area() { return 0; };
virtual char* Name() { return ""; };
};
class EquilateralTriangle : public GeometricFigure {
public:
EquilateralTriangle(double sideLength)
{
SideLength = sideLength;
}
char* Name() { return "Equilateral Triangle"; }
double Area() { return (sqrt(3) / 2 * pow(SideLength, 2)); }
};
In C++, the compiler reads your code from top-to-bottom, once. This is a holdover from when early C compilers only had a few kilobytes of memory to work with - C was designed so that a compiler would only need to look at a little bit of the code at a time.
Because of this, things must have been declared or defined as necessary, before you try to use them.
Move both classes somewhere before main. GeometricFigure must be before EquilateralTriangle, and EquilateralTriangle must be before main.
You would need to "declare" or tell the compiler, where to look for the EquilateralTriangle and GeometricFigure, "before" you use it first. you might want to take a look at the similar discussion at - C# declarations vs definitions
I am trying to send a array of 15 integers between two functions in C++. The first enables the user to enter taxi IDs and the second functions allows the user to delete taxi IDs from the array. However I am having an issue sending the array between the functions.
void startShift ()
{
int array [15]; //array of 15 declared
for (int i = 0; i < 15; i++)
{
cout << "Please enter the taxis ID: ";
cin >> array[i]; //user enters taxi IDs
if (array[i] == 0)
break;
}
cout << "Enter 0 to return to main menu: ";
cin >> goBack;
cout << "\n";
if (goBack == 0)
update();
}
void endShift ()
{
//need the array to be sent to here
cout << "Enter 0 to return to main menu: ";
cin >> goBack;
cout << "\n";
if (goBack == 0)
update();
}
Any help is great valued. Many thanks.
Since the array has been created on the stack, you would just need to pass the pointer to the first element, as an int*
void endshift(int* arr)
{
int val = arr[1];
printf("val is %d", val);
}
int main(void)
{
int array[15];
array[1] = 5;
endshift(array);
}
Since the array is created on the stack, it will no longer exist once the routine in which it was created has exited.
Declare the array outside of those functions and pass it to them by reference.
void startShift(int (&shifts)[15]) {
// ...
}
void endShift(int (&shifts)[15]) {
// ...
}
int main() {
int array[15];
startShift(array);
endShift(array);
}
This isn't exactly pretty syntax or all that common. A much more likely way to write this is to pass a pointer to the array and its length.
void startShift(int* shifts, size_t len) {
// work with the pointer
}
int main() {
int array[15];
startShift(array, 15);
}
Idiomatic C++ would be different altogether and use iterators to abstract away from the container, but I suppose that is out of scope here. The example anyway:
template<typename Iterator>
void startShift(Iterator begin, Iterator end) {
// work with the iterators
}
int main() {
int array[15];
startShift(array, array + 15);
}
You also wouldn't use a raw array, but std::array.
It won't work to use a local array in the startShift() function. You are best off to do one or more of the following:
Use an array in the function calling startShift() and endShift() and pass the array to these functions, e.g.:
void startShift(int* array) { ... }
void endShift(int* array) { ... }
int main() {
int arrray[15];
// ...
startShift(array);
// ...
endShift(array);
// ...
}
Don't use built-in arrays in the first place: use std::vector<int> instead: that class automatically maintains the current size of the array. You can also return it from a function altough you are probably still best off to pass the objects to the function.
void endShift (int* arr)
{
arr[0] = 5;
}
I have the following Python snippet that I would like to reproduce using C++:
from itertools import count, imap
source = count(1)
pipe1 = imap(lambda x: 2 * x, source)
pipe2 = imap(lambda x: x + 1, pipe1)
sink = imap(lambda x: 3 * x, pipe2)
for i in sink:
print i
I've heard of Boost Phoenix, but I couldn't find an example of a lazy transform behaving in the same way as Python's imap.
Edit: to clarify my question, the idea is not only to apply functions in sequence using a for, but rather to be able to use algorithms like std::transform on infinite generators. The way the functions are composed (in a more functional language like dialect) is also important, as the next step is function composition.
Update: thanks bradgonesurfing, David Brown, and Xeo for the amazing answers! I chose Xeo's because it's the most concise and it gets me right where I wanted to be, but David's was very important into getting the concepts through. Also, bradgonesurfing's tipped Boost::Range :).
Employing Boost.Range:
int main(){
auto map = boost::adaptors::transformed; // shorten the name
auto sink = generate(1) | map([](int x){ return 2*x; })
| map([](int x){ return x+1; })
| map([](int x){ return 3*x; });
for(auto i : sink)
std::cout << i << "\n";
}
Live example including the generate function.
I think the most idiomatic way to do this in C++ is with iterators. Here is a basic iterator class that takes an iterator and applies a function to its result:
template<class Iterator, class Function>
class LazyIterMap
{
private:
Iterator i;
Function f;
public:
LazyIterMap(Iterator i, Function f) : i(i), f(f) {}
decltype(f(*i)) operator* () { return f(*i); }
void operator++ () { ++i; }
};
template<class Iterator, class Function>
LazyIterMap<Iterator, Function> makeLazyIterMap(Iterator i, Function f)
{
return LazyIterMap<Iterator, Function>(i, f);
}
This is just a basic example and is still incomplete as it has no way to check if you've reached the end of the iterable sequence.
Here's a recreation of your example python code (also defining a simple infinite counter class).
#include <iostream>
class Counter
{
public:
Counter (int start) : value(start) {}
int operator* () { return value; }
void operator++ () { ++value; }
private:
int value;
};
int main(int argc, char const *argv[])
{
Counter source(0);
auto pipe1 = makeLazyIterMap(source, [](int n) { return 2 * n; });
auto pipe2 = makeLazyIterMap(pipe1, [](int n) { return n + 1; });
auto sink = makeLazyIterMap(pipe2, [](int n) { return 3 * n; });
for (int i = 0; i < 10; ++i, ++sink)
{
std::cout << *sink << std::endl;
}
}
Apart from the class definitions (which are just reproducing what the python library functions do), the code is about as long as the python version.
I think the boost::rangex library is what you are looking for. It should work nicely with the new c++lambda syntax.
int pipe1(int val) {
return 2*val;
}
int pipe2(int val) {
return val+1;
}
int sink(int val) {
return val*3;
}
for(int i=0; i < SOME_MAX; ++i)
{
cout << sink(pipe2(pipe1(i))) << endl;
}
I know, it's not quite what you were expecting, but it certainly evaluates at the time you want it to, although not with an iterator iterface. A very related article is this:
Component programming in D
Edit 6/Nov/12:
An alternative, still sticking to bare C++, is to use function pointers and construct your own piping for the above functions (vector of function pointers from SO q: How can I store function pointer in vector?):
typedef std::vector<int (*)(int)> funcVec;
int runPipe(funcVec funcs, int sinkVal) {
int running = sinkVal;
for(funcVec::iterator it = funcs.begin(); it != funcs.end(); ++it) {
running = (*(*it))(running); // not sure of the braces and asterisks here
}
return running;
}
This is intended to run through all the functions in a vector of such and return the resulting value. Then you can:
funcVec funcs;
funcs.pushback(&pipe1);
funcs.pushback(&pipe2);
funcs.pushback(&sink);
for(int i=0; i < SOME_MAX; ++i)
{
cout << runPipe(funcs, i) << endl;
}
Of course you could also construct a wrapper for that via a struct (I would use a closure if C++ did them...):
struct pipeWork {
funcVec funcs;
int run(int i);
};
int pipeWork::run(int i) {
//... guts as runPipe, or keep it separate and call:
return runPipe(funcs, i);
}
// later...
pipeWork kitchen;
kitchen.funcs = someFuncs;
int (*foo) = &kitchen.run();
cout << foo(5) << endl;
Or something like that. Caveat: No idea what this will do if the pointers are passed between threads.
Extra caveat: If you want to do this with varying function interfaces, you will end up having to have a load of void *(void *)(void *) functions so that they can take whatever and emit whatever, or lots of templating to fix the kind of pipe you have. I suppose ideally you'd construct different kinds of pipe for different interfaces between functions, so that a | b | c works even when they are passing different types between them. But I'm going to guess that that's largely what the Boost stuff is doing.
Depending on the simplicity of the functions :
#define pipe1(x) 2*x
#define pipe2(x) pipe1(x)+1
#define sink(x) pipe2(x)*3
int j = 1
while( ++j > 0 )
{
std::cout << sink(j) << std::endl;
}
I am sure this is a very simple fix and I feel dumb asking it but here it goes.
I need help with a struct and passing info from a gather function to a save or set function, and then passing it again to another function for further use.
Basically, it looks like this to start. I'll just add short snips of the code. All can be provided if you would like to see it.
I right now am just looking for the proper way to pass struct defined data from get.... to set.... functions.
struct printype
{
char dots[8][15];
int unknown15; // can have values of 0..127
string serial11_14; // 8 characters 00000000...99999999
int year8; // without century, 0..99
int month7; // 1..12
int day6; // 1..31
int hour5; // 0..23
int minute2; // 0..59
};
int getunknown15(); // prototypes
int setunknown15(int);
then we have a simple main.
int main()
{
printype pt;
pt.unknown15=getunknown15();
pt.unknown15=setunknown15(12);
pt.serial11_14=getserial11_14();
pt.serial11_14=setserial11_14("12345678");
pt.year8=getyear8();
pt.year8=setyear8(44);
pt.month7=getmonth7();
pt.month7=setmonth7(11);
pt.day6=getday6();
pt.day6=setday6(12);
pt.hour5=gethour5();
pt.hour5=sethour5(12);
pt.minute2=getminute2();
pt.minute2=setminute2(23);
cout <<"-----------------------------------------------------"<<endl;
cout <<" Let's Get Started"<<endl;
cout <<"-----------------------------------------------------"<<endl;
setup(pt.dots); // sets up the array
dpinfo(pt); // prints out the final array
ftarray(pt);
spar(pt.dots);
darray(pt.dots);
}
and finally the get and set array functions.
int getunknown15()
{
printype tem;
cout <<"-----------------------------------------------------"<<endl;
cout <<" Enter the Unkown Variable (0-127): ";
cin >>tem.unknown15;
cout <<"-----------------------------------------------------"<<endl;
return tem.unknown15;
}
next is
int setunknown15(int tem)
{
printype pp;
if (tem>127||tem<0)
{
cout << "Error" << endl;
return 0;
}
else
{
pp.unknown15 = tem;
return pp.unknown15;
}
}
I hope this isn't too much to read and understand
Anyway, I know this has a really simple answer but my brain just isn't working right now.
Edit: As StilesCrisis stated, Send struct as parameter is quiet stupid in this case. better use a const reference.
Well, I am not sure if I understand your question correctly. You can simply send struct to another function as parameter, or as a pointer.
like:
void SetStruct(const printype& var);
printype GetStruct();
Is it what you are looking for?
Please use the following access to the your fields, (by reference):
struct printype *myPtr = new printype;
myPtr->day6 = 43;
When use pointer instead of a normal variable, you should use -> instead . to access your fields.
I know this is kind of old but I thought I should give it a shot, since you are using C++ and it looks like you are trying to use some OO practices (I think), you don't need to start with a struct, even though OO principles can be applied using them as well though not as elegantly.
you can define your class header file as such.
#ifndef PRINTYPE_H
#define PRINTYPE_H
#include <string>
using namespace std;
class printype
{
private: // we always want to declare our member fields private for safety/managements reasons, no one will be able to access them outside.
char dots[8][15];
int unknown15; // can have values of 0..127
string serial11_14; // 8 characters 00000000...99999999
int year8; // without century, 0..99
int month7; // 1..12
int day6; // 1..31
int hour5; // 0..23
int minute2; // 0..59
void init(); // This is the method we use to initialize our starting state.
public: // This is our public methods, how people deal with/get/set our state.
printype(); // This is our default constructor
printype(const printype& print_type); // This our copy constructor
virtual ~printype(); // This is our destructor, its virtual, making safer for inheritance.
// This is our setters/getters
void setUnknown(int unknown);
int getUnknown();
void setYear(int year);
int getYear();
void setMonth(int mont);
int getMonth();
// and well you get the idea, you can add more methods.
};
#endif
and the accompanying class source file with your functions implementation
printype::printype()
{
this->init(); // Initialize all your vatiables, safer to just define a function to this.
}
printype::printype(const printype& orig) // copy constructor
{
this->setUknown(orig.getUnknown());
this->setDay(orig.getDay());
this->setDots(orig.getDots());
// you get the idea ...
}
printype::~printype()
{
// Have anything you need to do before destroying the object.
}
void printype::init()
{
this->setUnknwon(0);
this->setyear(0);
this->setMonth(1);
char dots[8][15] = {'\0'};
this->setDots(dots);
// you get the idea, you want to initialize all your variables since, for the most part they initially hold garbage.
}
void printype::setUnknown(int unknown)
{
if (unknown >= 0 && unknown < 127)
this->unknown15 = unknown;
else
error("Expecting unknown to be between 0 and 127"); // error should probably print the error and/or exit(-1) up to u
}
int printype::setYear(int year)
{
if (year >= 1 && year <= 99)
this->year8 = year;
else
error("Expecting year between 0 and 99"); // you may want to implement an error function!
}
int printype::getYear()
{
return this->year8;
}
void printype::setDots(char dots[8][15])
{
// you may want to do some verifications
memcpy(this->dots, dots, sizeof(dots));
}
void printype::setDots(char **dots) // this is a bit unsafe, use at your own risk.
{
if (dots)
{
unsigned int index = 0;
for (index = 0; index < 8; index++)
if (dots[index])
memcpy(this->dots[index], dots[index], 15);
else
error("dots required pointer ...");
}
else
error("dots required pointer ...");
}
char **getDots() // We will be returning a copy, we don't want the internal state to be affected, from outside, by using reference or pointers.
{
char **dots = new char*[8];
unsigned int index = 0;
for (index = 0; index < 8; index++)
{
dots[index] = new char[15];
memcpy(dots[index], this->dots[index], 15);
}
return dots;
}
// and well you get the idea ...
to use your class
printype *print_type_p = new print_type();
// or
printype pront_type_p();
// use the different public method to update the internal state.
print_type_p->setYear(3);
// or
print_type.setYear(3);
print_type_p->getYear();
// and so on.