Search results
A preprocessing directive of the form. # line digit-sequence " s-char-sequenceopt" new-line. sets the presumed line number similarly and changes the presumed name of the source file to be the contents of the character string literal. §16.4.5:
- Overview
- Remarks
- Example
The #line directive tells the preprocessor to set the compiler's reported values for the line number and filename to a given line number and filename.
The compiler uses the line number and optional filename to refer to errors that it finds during compilation. The line number usually refers to the current input line, and the filename refers to the current input file. The line number is incremented after each line is processed.
The digit-sequence value can be any integer constant within the range from 0 to 2147483647, inclusive. Macro replacement can be used on the preprocessing tokens, but the result must evaluate to the correct syntax. The filename can be any combination of characters and must be enclosed in double quotation marks (" "). If filename is omitted, the previous filename remains unchanged.
You can alter the source line number and filename by writing a #line directive. The #line directive sets the value for the line that immediately follows the directive in the source file. The translator uses the line number and filename to determine the values of the predefined macros __FILE__ and __LINE__. You can use these macros to insert self-descriptive error messages into the program text. For more information on these predefined macros, see Predefined macros.
The __FILE__ macro expands to a string whose contents are the filename, surrounded by double quotation marks (" ").
The following examples illustrate #line and the __LINE__ and __FILE__ macros.
In the first example, the line number is set to 10, then to 20, and the filename is changed to hello.cpp. In this example, the macro ASSERT uses the predefined macros __LINE__ and __FILE__ to print an error message about the source file if a given assertion isn't true.
Preprocessor directives are lines included in the code of programs preceded by a hash sign (#). These lines are not program statements but directives for the preprocessor. The preprocessor examines the code before actual compilation of code begins and resolves all these directives before any code is actually generated by regular statements.
Feb 7, 2010 · The #line directive in C is a preprocessor directive that lets you modify the compiler's reported values for the line number. Functionality: Changes the apparent line number of the current code section. Optionally updates the reported filename for compiler messages.
Dec 1, 2022 · 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.
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.
People also ask
What is a line directive in C++?
Can a line directive be inserted in a c++ file?
What is a line directive?
What are preprocessor directives?
What is a preprocessor line control directive?
What does __line__ do?
‘#line’ is a directive that specifies the original line number and source file name for subsequent input in the current preprocessor input file. ‘#line’ has three variants: #line linenum. linenum is a non-negative decimal integer constant. It specifies the line number which should be reported for the following line of input. Subsequent ...
