assignment to vector

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C++ Vector Library - assign() Function

Description.

The C++ function std::vector::assign() assign new values to the vector elements by replacing old ones. It modifies size of vector if necessary.

If memory allocation happens allocation is allocated by internal allocator.

Declaration

Following is the declaration for std::vector::assign() function form std::vector header.

n − Size of vector.

val − Value for each element.

Return value

This member function never throws exception.

Time complexity

Linear i.e. O(n)

The following example shows the usage of std::vector::assign() function.

Let us compile and run the above program, this will produce the following result −

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Vectors are part of the C++ Standard Template Library . To use vectors, we need to include the vector header file in our program.

• C++ Vector Declaration

Once we include the header file, here's how we can declare a vector in C++:

The type parameter <T> specifies the type of the vector. It can be any primitive data type such as int , char , float , etc. For example,

Here, num is the name of the vector.

Notice that we have not specified the size of the vector during the declaration. This is because the size of a vector can grow dynamically, so it is not necessary to define it.

• C++ Vector Initialization

There are different ways to initialize a vector in C++.

Here, we are initializing the vector by providing values directly to the vector. Now, both vector1 and vector2 are initialized with values 1 , 2 , 3 , 4 , 5 .

Here, 5 is the size of the vector and 12 is the value.

This code creates an int vector with size 5 and initializes the vector with the value of 12 . So, the vector is equivalent to

Example: C++ Vector Initialization

Here, we have declared and initialized three different vectors using three different initialization methods and displayed their contents.

Basic Vector Operations

The vector class provides various methods to perform different operations on vectors. We will look at some commonly used vector operations in this tutorial:

• Add elements
• Access elements
• Change elements
• Remove elements

1. Add Elements to a Vector

To add a single element into a vector, we use the push_back() function. It inserts an element into the end of the vector. For example,

Here, we have initialized an int vector num with the elements {1, 2, 3, 4, 5} . Notice the statements

Here, the push_back() function adds elements 6 and 7 to the vector.

Note : We can also use the insert() and emplace() functions to add elements to a vector.

2. Access Elements of a Vector

In C++, we use the index number to access the vector elements. Here, we use the at() function to access the element from the specified index. For example,

• num.at(0) - access element at index 0
• num.at(2) - access element at index 2
• num.at(4) - access element at index 4

Note: Like an array, we can also use the square brackets [] to access vector elements. For example,

However, the at() function is preferred over [] because at() throws an exception whenever the vector is out of bound, while [] gives a garbage value.

3. Change Vector Element

We can change an element of the vector using the same at() function. For example,

In the above example, notice the statements,

Here, we have assigned new values to indexes 1 and 4 . So the value at index 1 is changed to 9 and the value at index 4 is changed to 7 .

4. Delete Elements from C++ Vectors

To delete a single element from a vector, we use the pop_back() function. For example,

In the above example, notice the statement,

Here, we have removed the last element ( 7 ) from the vector.

• C++ Vector Functions

In C++, the vector header file provides various functions that can be used to perform different operations on a vector.

• C++ Vector Iterators

Vector iterators are used to point to the memory address of a vector element. In some ways, they act like pointers in C++.

We can create vector iterators with the syntax

For example, if we have 2 vectors of int and double types, then we will need 2 different iterators corresponding to their types:

Initialize Vector Iterators

We can initialize vector iterators using the begin() and end() functions.

1. begin() function

The begin() function returns an iterator that points to the first element of the vector. For example,

2. end() function

The end() function points to the theoretical element that comes after the final element of the vector. For example,

Here, due to the nature of the end() function, we have used the code num.end() - 1 to point to the last element of the num vector i.e. num[2] .

Example: C++ Vector Iterators

In this program, we have declared an int vector iterator iter to use it with the vector num .

Then, we initialized the iterator to the first element of the vector using the begin() function.

Then, we printed the vector element by dereferencing the iterator:

Then, we printed the 3rd element of the vector by changing the value of iter to num.begin() + 2 .

Finally, we printed the last element of the vector using the end() function.

• Example: Iterate Through Vector Using Iterators

Here, we have used a for loop to initialize and iterate the iterator iter from the beginning of the vector to the end of the vector using the begin() and end() functions.

Also Read :

Table of Contents

• Introduction
• Example: C++ Vector
• Add Elements to a Vector
• Access Elements of a Vector
• Change Vector Element
• Delete Elements from C++ Vectors

Sorry about that.

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std:: vector ::operator=

Return value, iterator validity, exception safety.

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Std::vector<t,allocator>:: operator=.

Replaces the contents of the container.

[ edit ] Parameters

[ edit ] return value, [ edit ] complexity, [ edit ] exceptions, [ edit ] notes.

After container move assignment (overload (2) ), unless element-wise move assignment is forced by incompatible allocators, references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in * this . The current standard makes this guarantee via the blanket statement in [container.reqmts]/67 , and a more direct guarantee is under consideration via LWG issue 2321 .

[ edit ] Example

The following code uses operator = to assign one std::vector to another:

[ edit ] See also

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<vector>

Std:: vector ::assign, return value, iterator validity, exception safety.

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Assign values to specified elements of signal

Libraries: Simulink / Math Operations HDL Coder / Math Operations

Description

The Assignment block assigns values to specified elements of the signal. You specify the indices of the elements to be assigned values either by entering the indices in the block dialog box or by connecting an external indices source or sources to the block. The signal at the block data port, U , specifies values to be assigned to Y . The block replaces the specified elements of Y with elements from the data signal.

Based on the value you enter for the Number of output dimensions parameter, a table of index options is displayed. Each row of the table corresponds to one of the output dimensions in Number of output dimensions . For each dimension, you can define the elements of the signal to work with. Specify a vector signal as a 1-D signal and a matrix signal as a 2-D signal. To enable an external index port, in the corresponding row of the table, set Index Option to Index vector (port) or Starting index (port) .

For example, assume a 5-D signal with a one-based index mode. The table in the Assignment block dialog changes to include one row for each dimension. If you define each dimension with the following entries:

The assigned values are Y(1:end,[1 3 5],4:3+size(U,3),Idx4:Idx4+size(U,4)-1,Idx5)=U , where Idx4 and Idx5 are the input ports for dimensions 4 and 5.

When using the Assignment block in normal mode, Simulink ® initializes block outputs to zero even if the model does not explicitly initialize them. In accelerator mode, Simulink converts the model into an S-Function. This involves code generation. The code generated may not do implicit initialization of block outputs. In such cases, you must explicitly initialize the model outputs.

You can use the block to assign values to vector, matrix, or multidimensional signals.

You can use an array of buses as an input signal to an Assignment block.

Assignment Block in Conditional Subsystem

If you place an Assignment block in a conditional subsystem block, a hidden signal buffer (which is equivalent to a Signal Copy block) is inserted in many cases, and merging of signals from Assignment blocks with partial writes can cause an error.

However, if you select the Ensure outport is virtual parameter for the conditional subsystem Outport block, such cases are supported and partial writes to arrays using Assignment blocks are possible. See Ensure Output Port Is Virtual .

Iterated Assignment with the Assignment Block

Using the Assignment block to assign values computed in a For or While Iterator loop to successive elements.

Parallel Channel Power Allocation

A potential use of the Find Nonzero Elements block. This block outputs a variable-size signal containing the indices of the nonzero values of the input.

Model Arrays of Buses

Use arrays of buses to represent structured data compactly.

Limitations

The Index parameter is not tunable during simulation. If the Index Option for a dimension is set to Index vector (dialog) or Starting index (dialog) and you specify a symbolic value, including a Simulink.Parameter object, for the corresponding Index in the block dialog, then the instantaneous value at the start of simulation will be used throughout the simulation, and the parameter will appear as an inlined value in the generated code. See Tune and Experiment with Block Parameter Values . You can adjust the assignment index dynamically by using index ports.

Y0 — Input initialization signal scalar | vector

The initialization signal for the output signal. If an element is not assigned another value, then the value of the output element matches this input signal value.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | fixed point | Boolean | enumerated | bus

U — Input data port scalar | vector

Value assigned to the output element when specified.

IndxN — N th index signal scalar | vector

External port specifying an index for the assignment of the corresponding output element.

You can specify integer of custom width (for example, a 15-bit integer or 23-bit integer) as an index signal value. When you configure the width of the integer, you must specify the Mode as Fixed point , with Word length less than or equal to 128, Slope equal to 1, and Bias equal to 0. For more information on specifying a fixed-point data type, see Specify Data Types Using Data Type Assistant .

Dependencies

To enable an external index port, in the corresponding row of the Index Option table, set Index Option to Index vector (port) or Starting index (port) .

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32

Y — Output signal with assigned values scalar | vector

The output signal with assigned values for the specified elements.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | fixed point | enumerated | bus

Number of output dimensions — Number of dimensions of the output signal 1 (default) | integer

Enter the number of dimensions of the output signal.

Programmatic Use

Index mode — index mode one-based (default) | zero-based.

Select the indexing mode. If One-based is selected, an index of 1 specifies the first element of the input vector. If Zero-based is selected, an index of 0 specifies the first element of the input vector.

Index Option — Index method for elements Index vector (dialog) (default) | Assign all | Index vector (port) | Starting index (dialog) | Starting index (port)

Define, by dimension, how the elements of the signal are to be indexed. From the list, select:

If you choose Index vector (port) or Starting index (port) for any dimension in the table, you can specify one of these values for the Initialize output (Y) parameter:

Initialize using input port <Y0>

Specify size for each dimension in table

Otherwise, Y0 always initializes output port Y .

The Index and Output Size columns are displayed as relevant.

Index — Index of elements 1 (default) | integer

If the Index Option is Index vector (dialog) , enter the index of each element you are interested in.

If the Index Option is Starting index (dialog) , enter the starting index of the range of elements to be selected. The number of elements from the starting point is determined by the size of this dimension at U .

Output Size — Width of block output signal 1 (default) | integer

Enter the width of the block output signal.

To enable this column, select Specify size for each dimension in table for the Initialize output (Y) parameter.

Initialize output (Y) — How to initialize output signal Initialize using input port <Y0> (default) | Specify size for each dimension in the table

Specify how to initialize the output signal.

Initialize using input port <Y0> – Signal at the input port Y0 initializes the output.

Specify size for each dimension in table – Requires you to specify the width of the block output signal in the Output Size parameter. If the output has unassigned elements, the value of those elements is undefined.

Enabled when you set Index Option to Index vector (port) or Starting index (port) for one or more dimensions.

Action if any output element is not assigned — Option to produce warning or error Warning (default) | Error | None

Specify whether to produce a warning or error if you have not assigned all output elements. Options include:

Warning — Simulink displays a warning and continues the simulation.

Error — Simulink terminates the simulation and displays an error.

None — Simulink takes no action.

To enable this parameter, set Index Option to Index vector (port) or Starting index (port) for one or more dimensions, then set Initialize output (Y) to Specify size for each dimension in table .

Sample time (-1 for inherited) — Interval between samples -1 (default) | scalar | vector

Specify the time interval between samples. To inherit the sample time, set this parameter to -1 . For more information, see Specify Sample Time .

This parameter is visible only if you set it to a value other than -1 . To learn more, see Blocks for Which Sample Time Is Not Recommended .

Check for out-of-range index in accelerated simulation — Option to check for out-of-range index values in accelerator and rapid accelerator simulation modes off (default) | on

Select this check box to have Simulink check during simulation in accelerator or rapid accelerator mode whether any index values are outside the range of valid indices for the relevant dimension of the input signal. If an index is out of range, Simulink stops the simulation and displays an error message.

If you do not select this check box, out-of-range index values could lead to undefined behavior during accelerator or rapid accelerator mode simulation.

Simulink performs this check during normal mode simulation regardless of whether you select this check box.

Block Characteristics

Extended capabilities, c/c++ code generation generate c and c++ code using simulink® coder™., hdl code generation generate vhdl, verilog and systemverilog code for fpga and asic designs using hdl coder™..

HDL Coder™ provides additional configuration options that affect HDL implementation and synthesized logic.

This block has one default HDL architecture.

This block supports code generation for complex signals.

Variable-size signals are not supported for code generation.

PLC Code Generation Generate Structured Text code using Simulink® PLC Coder™.

Fixed-point conversion design and simulate fixed-point systems using fixed-point designer™., version history, r2023a: index signal supports integer of custom width.

Starting in R2023a, you can customize the width of the integer that you use to specify the index signal value for the Assignment block.

Bus Assignment | Selector

• Group Nonvirtual Buses in Arrays of Buses

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Simple question about assignment to a vector of vectors

The result is not what I would expect. Instead, I would have expected to get

Can you explain to me what’s going on here, and why the result is not what I expect?

Another data point. When the vectors are different sizes, then I get the behavior I expect:

Ah yeah this tripped me up at first as well. If you look at the help page for fill :

All of the objects in A are the same (like pointing exactly to the same spot in memory). So when you update one, they all get updated.

I usually avoid this using a list comprehension:

Thanks for the help!

I guess I was confused because it didn’t occur to me that the internal fill(0,2) would be creating a new object that persists. I would have realized what’s happening if I had written this instead:

I think this is a really important thing for people to come to Julia (especially from R) to realize. In Julia, whenever you call f(g(x)) f only sees the result of g(x) , not how it got there. This is why macros have special syntax. In R, all functions are the equivalent of macros in Julia, which adds a ton of magic that makes code less predictable. In Julia, there is a special syntax that warns the reader that something special is happening when a macro is used.

@Oscar_Smith , could you please explain a bit further what this fill() 's behavior has to do with f(g(x)) , and why this is the most logical choice? It looks like another trap that is very easy to fall into. Thanks.

First, if all you want is a matrix, then fill(0, (2, 3)) suits your need. If you really want an array of arrays, then you have to create independent arrays for each entry in the larger array (usually with list comprehension).

For your question, fill([1], 3) could be interpreted as such:

• create an array that repeats a single object
• the object is [1] in this case
• this object will be repeated for 3 times
• fill does not attempt to make copies of this object

But array comprehension [[1] for i in 1:3] is not taking [1] as an argument, instead, it takes a function i->[1] that produces a distinct array that only contains 1 each time it is called.

see also fill(anArray,2) behaviour

I agree that the behavior of fill([0, 0], 2) is counterintuitive and kind of pointless. This question comes up on a regular basis here on Discourse. I would favor changing this behavior for Julia 2.0.

I just opened an issue that suggests changing the fill behavior for Julia version 2.0.

https://github.com/JuliaLang/julia/issues/41209

What is going on here?

What is going on here? Why didn’t I get:

a = fill(zeros(2), 2)

this creates a 2-element vector, where both elements refer to the same object, namely the newly created zeros(2) . i.e. a[1] refers to the same object as a[2] . This is the behaviour of fill .

If you modify (mutate) that object, the change will be reflected when referencing that object via either a[1] or a[2] (since it is the same object).

However, when you write a[1] = [1.0,1.0] , you are “reassigning” a[1] to refer to the newly created object [1.0,1.0] . Hence, a[1] and a[2] now refer to different objects.

I also stumbled in the same way. This can cause someone to waste many hours looking for errors in their code, while the mistake was to rely too much on their own intuition.

• Standard Template Library
• STL Priority Queue
• STL Interview Questions
• STL Cheatsheet
• C++ Templates
• C++ Functors
• C++ Iterators
• Common Subtleties in  Vector STLs
• std::partition in C++ STL
• How to transform Vector into String?
• equal_range in C++
• std::sort() in C++ STL
• std::string class in C++
• std::find_first_of in C++
• Sorting 2D Vector in C++ | Set 1 (By row and column)
• std::transform() in C++ STL (Perform an operation on all elements)
• How to convert C style strings to std::string and vice versa?
• How to sort a Vector in descending order using STL in C++?
• How to find common elements between two Vector using STL in C++?
• How to find the sum of elements of a Vector using STL in C++?
• std::move_backward in C++
• How to find the maximum element of a Vector using STL in C++?
• std::move in C++
• std::next_permutation and prev_permutation in C++
• std::find_if , std::find_if_not in C++
• std::count() in C++ STL

Ways to copy a vector in C++

In the case of arrays, there is not much choice to copy an array into another, other than the iterative method i.e running a loop to copy each element at its respective index. But Vector classes have more than one method for copying entire vectors into others in easier ways.

There are basically two types of copying:- 

Method 1: Iterative method. This method is a general method to copy, in this method a loop is used to push_back() the old vector elements into the new vector. They are deeply copied 

In the above code, changing the value at one vector did not alter the value at another vector, hence they are not allocated at the same address, hence deep copy.

Method 2: By assignment “=” operator . Simply assigning the new vector to the old one copies the vector. This way of assignment is not possible in the case of arrays. 

Method 3: By passing vector as constructor. At the time of declaration of vector, passing an old initialized vector copies the elements of the passed vector into the newly declared vector. They are deeply copied. 

Method 4: copy(first_iterator_o, last_iterator_o, back_inserter()) :- This is another way to copy old vector into new one. This function takes 3 arguments, first, the first iterator of the old vector, second, the last iterator of the old vector and third is back_inserter function to insert values from the back. This also generated a deep copy. 

Method 5: assign(first_iterator_o, last_iterator_o): This method assigns the same values to the new vector as the old one. This takes 2 arguments, the first iterator to the old vector and the last iterator to the old vector. This generates a deep copy. 

Method 6: By using insert function. The vector class has a standard function, insert() , that can insert elements from a specified range.

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