Filename and line information

 

C

Language

headers

Type support

Dynamic memory management

Error handling

Program utilities

Variadic function support

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

Technical Specifications

 

C language

ASCII chart

Basic concepts

translation phases

comment

identifier

scope

lifetime

name space

type

arithmetic types

object

main function

memory model

Keywords

Preprocessor

Statements

Expressions

Initialization

Declarations

Functions

Miscellaneous

history of C

Technical Specifications

 

Preprocessor

#if#ifdef#ifndef#else#elif#endif

#define#undef#,## operators

#include

#error

#pragma

#line

 

Changes the current line number and file name in the preprocessor.

Syntax

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

Explanation

1) Changes the current preprocessor line number to lineno. Occurrences 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. Occurrences of the macro __FILE__ beyond 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.

Notes

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

The line number following the directive #line __LINE__ is implementation-defined (there are two possible values that __LINE__ can expand to in this case: number of endlines seen so far, or number of endlines seen so far plus the endline that ends the #line directive)