C++ :: Passing Vectors To Functions As Arguments By Reference And Value
Mar 12, 2014
I have a program that is working very well when I pass C++ vectors as arguments to my functions by reference, but I get some compilation errors when try to make a modification. I am also posting the entire program and its output below. so that you can see what is going on. I have commented out the line that causes an error.(Some of the indentation that got corrupted when I copied the code to the browser.)
This program basically calculates the coefficients of a least square polynomial and then evaluates this polynomial at artificial data points and verifies that this actually reproduces the original data within reasonable floating point error.
The function that computes the coefficients of the least square polynomial is Code: vector<double> LSPVecValued_GSL( const int, const vector<float> &, const vector<float> &); and as you can see it returns a vector by value, and this vector contains the coefficients of the least square polynomial.
There is also a function that evaluates this polynomial by accepting a vector argument by reference : Code: float evaluate_polynomial(double, vector<double>& ) ; I have also created another version of the evaluation function which accepts the same vector argument by value: Code: float evaluate_polynomial_ByValue(double t, vector<double> vec_a) ; In the program I call the first evaluation function (whose vector argument is passed by reference) by first using an intermediate vector variable containing the coefficients, and then I pass this vector as an argument to the evaluation function, as follows:
Code:
vec_a = LSPVecValued_GSL( deg, vec_x , vec_y);
for(int j=0; j< n ; j=j+20 ) {
cout<<"x["<<j<<"] = " << vec_x[j] << " ,y["<<j<<"] = " << vec_y[j] <<" , p(x["<<j<<"]) ( EVALUATED FROM REFERENCE) = "
<< evaluate_polynomial( vec_x[j], vec_a) << endl; // This version works without error
[Code] .....
As you can see above, I am also able to call the second evaluation function (the one whose vector argument is passed by value) directly by plugging in the function LSPVecValued_GSL"(...)" and this works without error, and this is a one step process, only one line of code is involved.
However, I get a compilation error (line number 12 that I have commented out above) if I try to plug in the function "LSPVecValued_GSL(...)" into the first evaluation function that expects a vector argument by reference. I tried to put a "&" in front ofLSPVecValued_GSL but this did not fix the bug.
What syntax is appropriate to use the first evaluation function (which accepts a vector argument by reference) if I want to plug in the vector-valued function LeastSquarePolynomial_GSL directly in the the first version of the evaluation function which expects a vector argument by reference?
I have a 1wire program from maxim running in visual studio. There is this argument in the main function that requires the com port to be specified the command line. If I do pass it as "COM1" the program works as expected.
I don't want to depend on having to pass "COM1" in the command line and into main. I've tried creating a string for COM1 and passing it right into the if function but it doesn't work.
Code: int main(int argc, char **argv) { int len, addr, page, answer, i; int done = FALSE; SMALLINT bank = 1; uchar data[552];
I know that passing arguments by const instead of value is more efficient and allows us to avoid allocating a temporary local variable of the argument type. But is this always true? Or are there some cases when calling functions with constant arguments should be avoided? If so, is passing by pointer the most efficient way?
The lambda accepts no arguments, but it accesses increment by value and current by reference, the latter being used to store the next value to be set. This lambda has the side effect that current will be updated when generate is finished. The following lambda expression is similar, but without the side effect:
[=]()mutable->T{T result(current); current += increment; return result;} "
I dont exactly understand what side affect it is talking about. Wouldn't you want generate to update current? I understand how the second code fixes it though, just takes everything in the enclosing scope by value.
I am trying to make quicksort and binary search and I get error when I am passing dynamic array to argument. It also says error during initialization of the dynamic array.
I'm having some problems with a function. The function is supposed to find the two largest values in an array.
Code:
void find_two_largest( const int *a, int n, int *largest, int *second_largest){ largest = a; int temp; second_largest = a; for ( int i = 1; i < n; i++){ if (*(a + i) > *largest){ temp = *largest;
[Code]....
I don't see any mistake with the code of the function, but when I try to call it inside my program it only returns 0 for both largest and second_largest.
Code:
int *find_middle( int *a, int n); void find_two_largest(const int *a, int n, int *largest, int *second_largest); int main() { int n;
[Code]...
Do I have to declare the variables largest and second_largest as normal integer variables and then pass their addresses as arguments to find_largest or is that incorrect?
Code: void Class1::Func(shared_ptr<type1> parameter) { } or void Class1::Func(const shared_ptr<type1>& parameter) { } or Should I ever pass arguments/parameters to other objects using shared_ptr's or raw pointers?
Write a function write with variable number of arguments that takes a string first argument followed by any number of arguments of type double and prints on the screen a string formatted by the rules described below. The first argument may contain formats in curly braces of the form {index[:specifier]}, where the square brackets show optional parts (this is :specifier may be missing), and index is the sequence number of an argument of type double (starting from sequence number 0).
Rules for formatting: In the printed string the curly brackets and their content will be replaced by the argument with the given index, formatted according to the given format specifier. If the format specifier is missing, the argument will be printed with its default format. For example:
write("The number {0} is greater than {1}.", 5, -3); will print The number 5 is greater than -3.
write("There are no format specifiers here."); will print There are no format specifiers here.
The format specifiers and their meanings are listed in the following table
Specifier MeaningFormat Output for 1.62 Output for 2.0 none default {0}1.62 2 ccurrency{0:c}$1.62 $2.00 escientific{0:e}1.620000e+000 2.000000e+000 ffixed point{0:f}1.620000 2.000000 iround to int{0:i}2 2
Limitations: You may limit the maximum number of arguments your function can process to a certain value, for example 10.
Suggested extensions: -Add an optional alignment specification in the format , e.g., make the format of the form {index[,alignment][:specifier]}, where alignment is an integer specifying the width of the field in which the corresponding argument will be printed. If alignment is positive, align to the right, if it is negative, align to the left. -Accept an optional integer after the specifier letter, specifying the required precision in the output. For example, {0:f2} will print the number 1.6234 as 1.62, but {0:f5} will print it as 1.62340.
How to pass arguments from other functions to main. i want to write a program like nano well not exactly like nano editor. I have a function f_read(char* filename[]), and fopen() get filename[1] as file name and *filename[2] as "r" read mode and rest of the code will read from a file.
I want is this char filename[] to main(int argc , char argv[])
I have in my main(), a function that creates my arg object using boost/program_options.hpp i want to pass this object to another function using templates like this:
Code: template <typename Targ> void Count(Targ & arg){ MyObj<string> QueryTab(arg["input-file"].as<string>()); //line number is 352 ... }
However I get an error:
Code: ../include/Filter.hpp: In member function ‘void Count(Targ&)’: ../include/Filter.hpp:352:40: error: expected primary-expression before ‘>’ token ../include/Filter.hpp:352:42: error: expected primary-expression before ‘)’ token ... obviously it does not recognize my intention, what did I do wrong?
I make a class (it stands for an ARMA time series), and I have a method wich modifies some of its variables. In other part of my program I have a function wich receives one object of this class as a parameter and, at some point, it calls the method of the ARMA class to modify it; here is my deal I want to pass the ARMA class by reference to this function, because I want the variables of the instance I'm passing to be modified, not those of a copy the method uses. Also, I would like not to declare the function inside the class ARMA, cause I use it in other places too (it's basically a Nelder-Mead optimization what it performs).
Here is a code wich sketches what I've been trying, and exactly the error message I get is "modifyParameter has not been declared".
#include <iostream> #include <cstdlib> using namespace std; class ARMA{
I suspect the syntax of the declaration, but I am not sure what to do here? If I change the call to the function, then the array ( matrix ) is passed by value, and it takes forever:
Code: int read_files(std::string fname, int nCols, int nRows, ss_matrix_t ssMat ) // this takes ages ( it does compile and link )
I'm having trouble using a stack's functions when passing it by reference.
I'm currently messing around with passing a pointer to the stack instead, but to no avail.
The problem is in my placeInto function. I will label, in my code, where the program stops.
The program is an RPN Calculator, designed to receive keyboard input of an infix mathematical string, convert the infix string into a postfix mathematical string, and then solve the string. The program then outputs the postfix string and the solution.
The program loops through until closed via force-close, as was assigned.
*/ #include <iostream> #include <string> #include <stack> using namespace std; /////////////////////// // function prototypes // /////////////////////// // u = unfinished /* 1*/void welcome(); // welcome screen
Code: void function1(unsigned int var1); int main(void) { function1(-3); } void function1(unsigned int var1) { printf("%d", var1); }
The output is -3. how it happens the argument is unsigned but iam passing signed but still prints the signed value. My bigger question is how the arguments are handled if the passing parameters are different types compared to declaration.
Every time we pass an object to a function, and when the function ends and the object is not necessary anymore the destructor is called. if it's passing by value then a copy of the object is passed. if the object has a pointer inside of it so we implement the copy constructor to create a new pointed-variable so the original pointer will not get deleted.
so far so good. But what about passing an object to a non-member function by reference?
The language says that as soon as the function ends - the object will be deleted , because we passed by ref. that means that after the function ends - the object is not usable anymore! =What does that say? that in c++ you can't pass object by ref. because it will get deleted and un-uasable??
Varifying it with a compiler shows that the object is NOT deleted after the function ends.
I need to create a function in my program to open an input file and another function to open an output file and I need to use the files in other functions so Im trying to pass the stream object by reference but then i need a condition that tells the compiler not to reopen the file because then it will delete everything and make me input the file names again. Heres the two functions.
This actually should work, because it is passing address of polymorphisms object.I have tried changing prototype of test in Data.h, but failed.passing object address/pointers in C++.
I created the following code to pass the the variable 'inputVoltage' by reference to the function 'input'. It certainly works when I run the program, but I dont think it is a standard way of doing it, i.e. the use of '*' and '&' is not according to convention ? Or perhaps the way did it is acceptable ?
int input (double *inputVoltage); int main ( { double inputVoltage; input(&inputVoltage);
Suppose I have a stl vector of ints, and I want to pass a sub-range of that vector as an argument to a function. One way of doing that would be to copy the sub-range, and then pass that copy by reference, as follows:
Code: #include <vector> using namespace std; int MyFunction(vector<int> &a_vector) { // Do something return 0;
[Code] ....
However, it can be time-consuming to copy the elements between the two vectors if my_vector is large. So I'm wondering if it is possible to directly pass a sub-range of my_vector by reference, without having to create a new vector and manually copy over all of the relevant elements?
