/E (Preprocess to stdout)


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The latest version of this topic can be found at -E (Preprocess to stdout).

Preprocesses C and C++ source files and copies the preprocessed files to the standard output device.


In this 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) compiler option as well.

/E 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.

The /E option suppresses compilation. You must resubmit the preprocessed file for compilation. /E 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 suppress #line directives, use the /EP (Preprocess to stdout Without #line Directives) option instead.

To send the preprocessed output to a file instead of to stdout, use the /P (Preprocess to a File) option instead.

To suppress #line directives and send the preprocessed output to a file, use /P and /EP together.

You cannot use precompiled headers with the /E option.

Note that when preprocessing to a separate file, spaces are not emitted after tokens. This can result in an illegal program or have unintended side effects. The following program compiles successfully:

#define m(x) x  
m(int)main( )  
   return 0;  

However, if you compile with:

cl -E test.cpp > test2.cpp  

int main in test2.cpp will incorrectly be intmain.

To set this compiler option in the Visual Studio development environment

  1. Open the project's Property Pages dialog box. For details, see How to: Open Project Property Pages.

  2. Click the C/C++ folder.

  3. Click the Command Line property page.

  4. Type the compiler option in the Additional Optionsbox.

To set this compiler option programmatically

The following command line preprocesses ADD.C, preserves comments, adds #line directives, and displays the result on the standard output device:

CL /E /C ADD.C  

Compiler Options
Setting Compiler Options