goto statement

 

哋它亢++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (哋它亢++20)

Language support library

Concepts library (哋它亢++20)

Metaprogramming library (哋它亢++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (哋它亢++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (哋它亢++17)

Regular expressions library (哋它亢++11)

Concurrency support library (哋它亢++11)

Technical specifications

Symbols index

External libraries

 

哋它亢++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (哋它亢++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function expression
inline specifier
Dynamic exception specifications (until 哋它亢++17*)
noexcept specifier (哋它亢++11)
Exceptions
throw-expression try block	handler
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Class/struct types Union types
Specifiers
const/volatile decltype (哋它亢++11) auto (哋它亢++11)	constexpr (哋它亢++11) consteval (哋它亢++20) constinit (哋它亢++20)
Storage duration specifiers
Initialization
Default-initialization Value-initialization Zero-initialization Copy-initialization Direct-initialization	Aggregate initialization List-initialization (哋它亢++11)       Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (哋它亢++11)
User-defined (哋它亢++11)
Utilities
Attributes (哋它亢++11)
Types
typedef declaration
Type alias declaration (哋它亢++11)
Casts
Implicit conversions static_cast const_cast	Explicit conversions dynamic_cast reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Constructors this pointer	Access specifiers friend specifier
Class-specific function properties
Virtual function override specifier (哋它亢++11)     final specifier (哋它亢++11)	explicit (哋它亢++11) static
Special member functions
Default constructor Copy constructor Move constructor (哋它亢++11)	Copy assignment Move assignment (哋它亢++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (哋它亢++11)
Miscellaneous
Inline assembly	History of 哋它亢++

 

Statements

Labels

label : statement

Expression statements

expression ;

Compound statements

{ statement... }

Selection statements

if

switch

Iteration statements

while

do while

for

range for (哋它亢++11)

Jump statements

break

continue

return

goto

Declaration statements

declaration ;

Try blocks

try block

Transactional memory

synchronized, atomic_commit, etc (TM TS)

 

Transfers control unconditionally.

Used when it is otherwise impossible to transfer control to the desired location using other statements.

Syntax

attr (optional) goto label ;

Explanation

The goto statement transfers control to the location specified by label. The goto statement must be in the same function as the label it is referring, it may appear before or after the label.

If transfer of control exits the scope of any automatic variables (e.g. by jumping backwards to a point before the declarations of such variables or by jumping forward out of a compound statement where the variables are scoped), the destructors are called for all variables whose scope was exited, in the order opposite to the order of their construction.

The goto statement cannot transfer control into a control-flow-limited statement, but can transfer control out of a control-flow-limited statement (the rules above regarding automatic variables in scope are followed).

If transfer of control enters the scope of any automatic variables (e.g. by jumping forward over a declaration statement), the program is ill-formed (cannot be compiled), unless all variables whose scope is entered have the following types:

• scalar types declared without initializers
• class types with trivial default constructors and trivial destructors declared without initializers
• cv-qualified versions of one of the above
• arrays of one of the above

(Note: the same rules apply to all forms of transfer of control)

Keywords

goto

Notes

In the C programming language, the goto statement has fewer restrictions and can enter the scope of any variable other than variable-length array or variably-modified pointer.

Example

Run this code

#include <iostream>
 
struct Object
{
    // non-trivial destructor
    ~Object() { std::cout << 'd'; }
};
 
struct Trivial
{
    double d1;
    double d2;
}; // trivial ctor and dtor
 
int main()
{
    int a = 10;
 
    // loop using goto
label:
    Object obj;
    std::cout << a << ' ';
    a -= 2;
 
    if (a != 0)
        goto label;  // jumps out of scope of obj, calls obj destructor
    std::cout << '\n';
 
    // goto can be used to efficiently leave a multi-level (nested) loops
    for (int x = 0; x < 3; ++x)
        for (int y = 0; y < 3; ++y)
        {
            std::cout << '(' << x << ',' << y << ") " << '\n';
            if (x + y >= 3)
                goto endloop;
        }
 
endloop:
    std::cout << '\n';
 
    goto label2; // jumps into the scope of n and t
 
    [[maybe_unused]] int n; // no initializer
 
    [[maybe_unused]] Trivial t; // trivial ctor/dtor, no initializer
 
//  int x = 1;   // error: has initializer
//  Object obj2; // error: non-trivial dtor
 
label2:
    {
        Object obj3;
        goto label3; // jumps forward, out of scope of obj3
    }
 
label3:
    std::cout << '\n';
}

Output:

10 d8 d6 d4 d2
(0,0)
(0,1)
(0,2)
(1,0)
(1,1)
(1,2)
 
d
d

External links

The popular Edsger W. Dijkstra essay, “Goto Considered Harmful” (originally, in "Letter to Communications of the ACM (CACM)", vol. 11 #3, March 1968, pp. 147-148.), presents a survey of the many subtle problems the careless use of this keyword can introduce.