/ | ||||
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(C++20) | ||||
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(C++11) | ||||
expression |
pointer |
specifier | ||||
specifier (C++11) | ||||
specifier (C++11) |
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(C++11) | ||||
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General | ||||
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(C++11) |
-expression | ||||
-expression | ||||
-expression |
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(C++17) | ||||
(C++20) |
Assignment operators modify the value of the object.
Operator name | Syntax | Prototype examples (for class T) | ||
---|---|---|---|---|
Inside class definition | Outside class definition | |||
simple assignment | Yes | T& T::operator =(const T2& b); | ||
addition assignment | Yes | T& T::operator +=(const T2& b); | T& operator +=(T& a, const T2& b); | |
subtraction assignment | Yes | T& T::operator -=(const T2& b); | T& operator -=(T& a, const T2& b); | |
multiplication assignment | Yes | T& T::operator *=(const T2& b); | T& operator *=(T& a, const T2& b); | |
division assignment | Yes | T& T::operator /=(const T2& b); | T& operator /=(T& a, const T2& b); | |
remainder assignment | Yes | T& T::operator %=(const T2& b); | T& operator %=(T& a, const T2& b); | |
bitwise AND assignment | Yes | T& T::operator &=(const T2& b); | T& operator &=(T& a, const T2& b); | |
bitwise OR assignment | Yes | T& T::operator |=(const T2& b); | T& operator |=(T& a, const T2& b); | |
bitwise XOR assignment | Yes | T& T::operator ^=(const T2& b); | T& operator ^=(T& a, const T2& b); | |
bitwise left shift assignment | Yes | T& T::operator <<=(const T2& b); | T& operator <<=(T& a, const T2& b); | |
bitwise right shift assignment | Yes | T& T::operator >>=(const T2& b); | T& operator >>=(T& a, const T2& b); | |
this, and most also return *this so that the user-defined operators can be used in the same manner as the built-ins. However, in a user-defined operator overload, any type can be used as return type (including void). can be any type including . |
Definitions Assignment operator syntax Built-in simple assignment operator Assignment from an expression Assignment from a non-expression initializer clause Built-in compound assignment operator Example Defect reports See also |
Copy assignment replaces the contents of the object a with a copy of the contents of b ( b is not modified). For class types, this is performed in a special member function, described in copy assignment operator .
replaces the contents of the object a with the contents of b, avoiding copying if possible (b may be modified). For class types, this is performed in a special member function, described in . | (since C++11) |
For non-class types, copy and move assignment are indistinguishable and are referred to as direct assignment .
Compound assignment replace the contents of the object a with the result of a binary operation between the previous value of a and the value of b .
The assignment expressions have the form
target-expr new-value | (1) | ||||||||
target-expr op new-value | (2) | ||||||||
target-expr | - | the expression to be assigned to |
op | - | one of *=, /= %=, += -=, <<=, >>=, &=, ^=, |= |
new-value | - | the expression (until C++11) (since C++11) to assign to the target |
If new-value is not an expression, the assignment expression will never match an overloaded compound assignment operator. | (since C++11) |
For the built-in simple assignment, the object referred to by target-expr is modified by replacing its value with the result of new-value . target-expr must be a modifiable lvalue.
The result of a built-in simple assignment is an lvalue of the type of target-expr , referring to target-expr . If target-expr is a bit-field , the result is also a bit-field.
If new-value is an expression, it is implicitly converted to the cv-unqualified type of target-expr . When target-expr is a bit-field that cannot represent the value of the expression, the resulting value of the bit-field is implementation-defined.
If target-expr and new-value identify overlapping objects, the behavior is undefined (unless the overlap is exact and the type is the same).
If the type of target-expr is volatile-qualified, the assignment is deprecated, unless the (possibly parenthesized) assignment expression is a or an . | (since C++20) |
new-value is only allowed not to be an expression in following situations: is of a , and new-value is empty or has only one element. In this case, given an invented variable t declared and initialized as T t = new-value , the meaning of x = new-value is x = t. is of class type. In this case, new-value is passed as the argument to the assignment operator function selected by . <double> z; z = {1, 2}; // meaning z.operator=({1, 2}) z += {1, 2}; // meaning z.operator+=({1, 2}) int a, b; a = b = {1}; // meaning a = b = 1; a = {1} = b; // syntax error | (since C++11) |
In overload resolution against user-defined operators , for every type T , the following function signatures participate in overload resolution:
& operator=(T*&, T*); | ||
volatile & operator=(T*volatile &, T*); | ||
For every enumeration or pointer to member type T , optionally volatile-qualified, the following function signature participates in overload resolution:
operator=(T&, T); | ||
For every pair A1 and A2 , where A1 is an arithmetic type (optionally volatile-qualified) and A2 is a promoted arithmetic type, the following function signature participates in overload resolution:
operator=(A1&, A2); | ||
The behavior of every built-in compound-assignment expression target-expr op = new-value is exactly the same as the behavior of the expression target-expr = target-expr op new-value , except that target-expr is evaluated only once.
The requirements on target-expr and new-value of built-in simple assignment operators also apply. Furthermore:
In overload resolution against user-defined operators , for every pair A1 and A2 , where A1 is an arithmetic type (optionally volatile-qualified) and A2 is a promoted arithmetic type, the following function signatures participate in overload resolution:
operator*=(A1&, A2); | ||
operator/=(A1&, A2); | ||
operator+=(A1&, A2); | ||
operator-=(A1&, A2); | ||
For every pair I1 and I2 , where I1 is an integral type (optionally volatile-qualified) and I2 is a promoted integral type, the following function signatures participate in overload resolution:
operator%=(I1&, I2); | ||
operator<<=(I1&, I2); | ||
operator>>=(I1&, I2); | ||
operator&=(I1&, I2); | ||
operator^=(I1&, I2); | ||
operator|=(I1&, I2); | ||
For every optionally cv-qualified object type T , the following function signatures participate in overload resolution:
& operator+=(T*&, ); | ||
& operator-=(T*&, ); | ||
volatile & operator+=(T*volatile &, ); | ||
volatile & operator-=(T*volatile &, ); | ||
Possible output:
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
C++11 | for assignments to class type objects, the right operand could be an initializer list only when the assignment is defined by a user-defined assignment operator | removed user-defined assignment constraint | |
C++11 | E1 = {E2} was equivalent to E1 = T(E2) ( is the type of ), this introduced a C-style cast | it is equivalent to E1 = T{E2} | |
C++20 | compound assignment operators for volatile -qualified types were inconsistently deprecated | none of them is deprecated | |
C++11 | an assignment from a non-expression initializer clause to a scalar value would perform direct-list-initialization | performs copy-list- initialization instead | |
C++20 | bitwise compound assignment operators for volatile types were deprecated while being useful for some platforms | they are not deprecated |
Operator precedence
Operator overloading
Common operators | ||||||
---|---|---|---|---|---|---|
a = b | ++a | +a | !a | a == b | a[...] | function call |
a(...) | ||||||
comma | ||||||
a, b | ||||||
conditional | ||||||
a ? b : c | ||||||
Special operators | ||||||
converts one type to another related type |
for Assignment operators |
Assignment operators are used to assigning the result of an expression to a variable. Up to now, we have used the shorthand assignment operator “=”, which assigns the result of a right-hand expression to the left-hand variable. For example, in the expression x = y + z, the sum of y and z is assigned to x.
Another form of assignment operator is variable operator_symbol= expression ; which is equivalent to variable = variable operator_symbol expression;
We have the following different types of assignment and assignment short-hand operators.
Expression with an assignment operator | Detailed expression with an assignment operator |
---|---|
x += y; | x = x + y; |
x -= y; | x = x – y; |
x /= y; | x = x / y; |
x *= y; | x = x * y; |
x %= y; | x = x % y; |
x &= y; | x = x & y; |
x |= y; | x = x | y; |
x ^= y; | x = x ^ y; |
x >>= y; | x = x >> y; |
x <<= y; | x = x << y; |
Expected Output:
C functions, c dynamic memory, c structure union, c file handling, c preprocessor, c command line, c programming test, c interview.
There are different kinds of the operators, such as arithmetic, relational, bitwise, assignment, etc., in the C programming language. The assignment operator is used to assign the value, variable and function to another variable. Let's discuss the various types of the assignment operators such as =, +=, -=, /=, *= and %=.
It is the operator used to assign the right side operand or variable to the left side variable.
Let's create a program to use the simple assignment operator in C.
The operator is used to add the left side operand to the left operand and then assign results to the left operand.
Let's create a program to use the Plus and assign operator in C.
The operator is used to subtract the left operand with the right operand and then assigns the result to the left operand.
Let's create a program to use the Subtract and Assign (-=) operator in C.
The operator is used to multiply the left operand with the right operand and then assign result to the left operand.
Let's create a program to use the multiply and assign operator (*=) in C.
An operator is used between the left and right operands, which divides the first number by the second number to return the result in the left operand.
Let's create a program to use the divide and assign operator (/=) in C.
An operator used between the left operand and the right operand divides the first number (n1) by the second number (n2) and returns the remainder in the left operand.
Let's create a program to use the divide and assign operator (%=) in C.
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The Awk command series is getting exciting! I believe that, in the previous seven parts, we walked through some fundamentals of Awk that you need to master to enable you to perform basic text or string filtering in Linux.
Starting with this part, we shall dive into advanced areas of Awk to handle more complex text or string filtering operations. Therefore, we will cover Awk features such as variables , numeric expressions , and assignment operators .
These concepts are not significantly different from those you may have encountered in many programming languages before, such as Shell, C, Python, and many others. So, there is no need to worry much about this topic; we are simply revising the common ideas of using these features.
This will probably be one of the easiest Awk command sections to understand, so sit back and let’s get going
In any programming language, a variable is a placeholder that stores a value . When you create a variable in a program file, as the file is executed, some space is created in memory that will store the value you specify for the variable.
You can define Awk variables in the same way you define shell variables as follows:
In the syntax above:
Let’s look at some examples below:
Take a look at the simple examples above, in the first variable definition, the value tecmint.com is assigned to the variable computer_name .
Furthermore, the value 22 is assigned to the variable port_no , it is also possible to assign the value of one variable to another variable as in the last example where we assigned the value of computer_name to the variable server.
If you can recall, right from part 2 of this Awk series , where we covered field editing, we talked about how Awk divides input lines into fields and uses a standard field access operator, $ to read the different fields that have been parsed. We can also use variables to store the values of fields as follows.
In the examples above, the value of first_name is set to the second field and second_name is set to the third field.
As an illustration, consider a file named names.txt which contains a list of users indicating their first and last names plus gender.
Using the cat command , we can view the contents of the file as follows
Then, we can also use the variables first_name and second_name to store the first and second names of the first user on the list as by running the Awk command below:
Let us also take a look at another case, when you issue the command uname -a on your terminal, it prints out all your system information.
The second field contains your hostname , therefore we can store the hostname in a variable called hostname and print it using Awk as follows:
In Awk , numeric expressions are built using the following numeric operators:
The syntax for a numeric expression is:
In the form above, operand1 and operand2 can be numbers or variable names, and operator is any of the operators above.
Below are some examples to demonstrate how to build numeric expressions:
To understand the use of numeric expressions in Awk , we shall consider the following example below, with the file domains.txt which contains all domains owned by Tecmint .
To view the contents of the file, use the command below:
If we want to count the number of times the domain tecmint.com appears in the file, we can write a simple script to do that as follows:
After creating the script, save it and make it executable, when we run it with the file, domains.txt as our input, we get the following output:
From the output of the script, there are 6 lines in the file domains.txt which contain tecmint.com , to confirm that you can manually count them.
The last Awk feature we shall cover is assignment operators, there are several assignment operators in Awk and these include the following:
The simplest syntax of an assignment operation in Awk is as follows:
You can use the assignment operators above to shorten assignment operations in Awk , consider the previous examples, we could perform the assignment in the following form:
Therefore, we can alter the Awk command in the shell script we just wrote above using += assignment operator as follows:
In this segment of the Awk command series , we covered some powerful Awk features, that is variables, building numeric expressions, and using assignment operators, plus a few illustrations of how we can actually use them.
These concepts are not any different from the ones in other programming languages but there may be some significant distinctions under Awk programming.
In part 9 , we shall look at more Awk features that are special patterns: BEGIN and END . Until then, stay connected to Tecmint .
For those seeking a comprehensive resource, we’ve compiled all the Awk series articles into a book, that includes 13 chapters and spans 41 pages, covering both basic and advanced Awk usage with practical examples.
Product Name | Price | Buy |
---|---|---|
eBook: Introducing the Awk Getting Started Guide for Beginners | $8.99 |
Hey TecMint readers ,
Exciting news! Every month, our top blog commenters will have the chance to win fantastic rewards, like free Linux eBooks such as RHCE , RHCSA , LFCS , Learn Linux , and Awk , each worth $20 !
Learn more about the contest and stand a chance to win by sharing your thoughts below !
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Each tutorial at TecMint is created by a team of experienced Linux system administrators so that it meets our high-quality standards.
How to Use Awk Special Patterns ‘BEGIN and END’ – Part 9
How to Read and Filter Awk Input from STDIN in Linux – Part 7
How to Use ‘next’ Command with Awk in Linux – Part 6
How to Use Compound Expressions with Awk in Linux – Part 5
How to Use Comparison Operators & Data Filtering with Awk – Part 4
How to Use Awk for Text Filtering with Pattern-Specific Actions – Part 3
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Operator overloading in C++ allows us to define custom behaviors for operators when applied to user-defined types. One of the most commonly overloaded operators is the assignment operator (=), which is used to assign the value of one object to another. However, when overloading the assignment operator, it’s important to ensure that it returns a reference to the object being assigned. But why is this necessary?
In this article, we will learn why the assignment operator must return a reference in C++ when overloading, and what could go wrong if it doesn’t.
When overloading the assignment operator in C++ , it’s important that it returns a reference to the object being assigned. There are several key reasons for this:
In C++, assignment operations can be chained together.
For example:
To support this chaining, the assignment operator must return a reference to the object being assigned. This allows the operation b = c to return b, enabling a = b to work as expected.
For built-in types, the assignment operator in C++ returns a reference to the left-hand operand. To maintain consistency and intuitive behavior for user-defined types, overloaded assignment operators should also return a reference.
If the assignment operator returned an object by value instead of by reference, it would result in the creation of a temporary object, which is immediately discarded. This unnecessary copying is inefficient and could lead to performance issues, especially for large objects or objects managing dynamic resources.
The below example demonstartes how to properly overload the assignment operator in C++.
If we overload the assignment operator and return by value instead of by reference, several issues could arise:
In C++, when overloading the assignment operator, we must return a reference to the current object ( *this ) as it allows for assignment chaining, maintains consistency with built-in types, and avoids unnecessary object copying. By following these best practice, we can ensure that our overloaded operators are efficient, intuitive, and behave as expected, making our C++ programs more robust and maintainable.
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