/P (Preprocess to a File)

Preprocesses C and C++ source files and writes the preprocessed output to a file.




The file has the same base name as the source file and an .i extension. In the process, all preprocessor directives are carried out, macro expansions are performed, and comments are removed. To preserve comments in the preprocessed output, use the /C (Preserve Comments During Preprocessing) option along with /P.

/P adds #line directives to the output, at the beginning and end of each included file and around lines removed by preprocessor directives for conditional compilation. These directives renumber the lines of the preprocessed file. As a result, errors generated during later stages of processing refer to the line numbers of the original source file rather than lines in the preprocessed file. To suppress the generation of #line directives, use /EP (Preprocess to stdout Without #line Directives) as well as /P.

The /P option suppresses compilation. It does not produce an .obj file, even if you use /Fo (Object File Name). You must resubmit the preprocessed file for compilation. /P also suppresses the output files from the /FA, /Fa, and /Fm options. For more information, see /FA, /Fa (Listing File) and /Fm (Name Mapfile).

To set this compiler option in the Visual Studio development environment

  1. Open the project's Property Pages dialog box. For details, see Set C++ compiler and build properties in Visual Studio.

  2. Select the Configuration Properties > C/C++ > Preprocessor property page.

  3. Modify the Generate Preprocessed File property.

To set this compiler option programmatically


The following command line preprocesses ADD.C, preserves comments, adds #line directives, and writes the result to a file, ADD.I:


See also

MSVC Compiler Options
MSVC Compiler Command-Line Syntax
/Fi (Preprocess Output File Name)