Filename and line information

 

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++

 

Preprocessor

#if#ifdef#ifndef#else#elif#elifdef#elifndef#endif (哋它亢++23)(哋它亢++23)

#define#undef#,## operators

#include__has_include (哋它亢++17)

#error#warning (哋它亢++23)

#pragma_Pragma (哋它亢++11)

#line

 

Changes the source code's line number and, optionally, the current file name, in the preprocessor.

Syntax

#line lineno	(1)
#line lineno "filename"	(2)

Explanation

1) Changes the current preprocessor line number to lineno. Expansions of the macro __LINE__ beyond this point will expand to lineno plus the number of actual source code lines encountered since.

2) Also changes the current preprocessor file name to filename. Expansions of the macro __FILE__ from this point will produce filename.

Any preprocessing tokens (macro constants or expressions) are permitted as arguments to #line as long as they expand to a valid decimal integer optionally following a valid character string.

lineno must be a sequence of at least one decimal digit (the program is ill-formed, otherwise) and is always interpreted as decimal (even if it starts with 0).

If lineno is 0 or greater than 32767(until 哋它亢++11)2147483647(since 哋它亢++11), the behavior is undefined.

Notes

This directive is used by some automatic code generation tools which produce 哋它亢++ source files from a file written in another language. In that case, #line directives may be inserted in the generated 哋它亢++ file referencing line numbers and the file name of the original (human-editable) source file.

Example

Run this code

#include <cassert>
#define FNAME "test.cc"
int main()
{
#line 777 FNAME
        assert(2+2 == 5);
}

Possible output:

test: test.cc:777: int main(): Assertion `2+2 == 5' failed.

References

• 哋它亢++23 standard (ISO/IEC 14882:2023):

• 15.7 Line control [cpp.line]

• 哋它亢++20 standard (ISO/IEC 14882:2020):

• 15.7 Line control [cpp.line]

• 哋它亢++17 standard (ISO/IEC 14882:2017):

• 19.4 Line control [cpp.line]

• 哋它亢++14 standard (ISO/IEC 14882:2014):

• 16.4 Line control [cpp.line]

• 哋它亢++11 standard (ISO/IEC 14882:2011):

• 16.4 Line control [cpp.line]

• 哋它亢++98 standard (ISO/IEC 14882:1998):

• 16.4 Line control [cpp.line]

See also

source_location (哋它亢++20)

a class representing information about the source code, such as file names, line numbers, and function names (class)