nuttx-apps/testing/cxxsize

C++ Standard Library Code Size Testing Program

Introduction

This project provides a testing program designed to measure the code size of each class in the C++ Standard Library. Understanding the code size of various classes can help developers optimize their usage of the standard library and make informed design decisions in their applications. This program aims to provide clear insights into how much memory each component of the standard library consumes, categorized into text, data, BSS, and overall size (DEC).

Purpose

The primary goals of this project are to:

• Analyze the memory consumption of standard library components.
• Identify potential areas for optimization in applications that utilize these components.
• Aid developers in making better decisions regarding the use of the C++ Standard Library depending on their application’s constraints.

Testing Platform

This program has been tested on the x4b/release branch.

C++ Compilation Configurations

• CONFIG_HAVE_CXX
• CONFIG_HAVE_CXXINITIALIZE
• CONFIG_LIBCXX
• CONFIG_LIBSUPCXX

Optimization Configurations

• CONFIG_DEBUG_OPTLEVEL="-Os"
• CONFIG_LTO_FULL
• -ffunction-section
• -fdata-section

Component-Specific Configurations

• iostream: enable CONFIG_LIBC_LOCALE.
• exception: enable CONFIG_CXX_EXCEPTION.
• rtti: enable CONFIG_CXX_RTTI.

Compilation Instructions

To compile the code size testing program, use the following command:

./build.sh qemu-armv7a:nsh -j

Code Size Breakdown

The following table summarizes the code size measurements for different components in the C++ Standard Library. The sizes are measured in bytes and broken down into the following categories:

• Text: Size of the code segment containing executable instructions.
• Data: Size of initialized global and static variables.
• BSS: Size of uninitialized global and static variables.
• DEC: Total size in bytes (sum of Text, Data, and BSS).

Output Examples

Without C++ Config

   text    data     bss     dec     hex filename
 204388     300    9728  214416   34590 nuttx/nuttx

Only Basic C++ Configurations

   text    data     bss     dec     hex filename
 208100     300    9856  218256   35490 nuttx/nuttx

Compiling an Empty main Function with Basic C++ Configurations

   text    data     bss     dec     hex filename
 208132     300    9856  218288   354b0 nuttx/nuttx

Code Size Measurements

Component	Text	Data	BSS	DEC
basic c++	3712	0	128	3840
array	32	0	0	32
condition_variable	584	8	16	608
deque	41196	300	40	41544
exception	32	0	32	32
forward_list	41164	308	40	41512
future	43504	356	112	43972
iostream	148004	404	3160	151568
list	41516	308	40	41864
map	45252	308	40	45600
multiset	44676	308	40	45024
mutex	552	8	16	576
rtti	41420	308	40	41768
semaphore	1352	8	16488	17808
set	44644	308	40	44992
shared_ptr	43204	308	40	41712
string	42044	308	40	42392
string_view	448	0	0	448
thread	41956	356	12	42424
unordered_map	47668	308	40	48016
unordered_multimap	46868	308	40	47216
unordered_multiset	46836	308	40	47184
unordered_set	46452	308	40	46800
vector	41444	308	40	41792
weak_ptr	43460	308	40	41936

Conclusion

By analyzing the code size of each component in the C++ Standard Library, developers can better understand the memory implications of their usage of these classes. The details provided in this README serve as a reference point for optimizing application performance and making educated design choices. We hope you find this information valuable as you work with the C++ Standard Library.