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	16	0	0	16
condition_variable	144	0	0	144
deque	240	0	8	248
exception	16	0	0	16
forward_list	144	0	8	152
future	3920	48	72	4040
iostream	66192	120	1704	68016
list	528	0	8	536
map	4256	0	8	4264
multiset	3680	0	8	3688
mutex	112	0	0	112
rtti	2208	0	8	2216
semaphore	1300	12	84	1392
set	3616	0	8	3624
shared_ptr	464	0	8	472
string_view	432	0	0	432
string	1376	0	8	1384
thread	1040	48	72	1160
unordered_map	6616	0	0	6616
unordered_multimap	5864	0	0	5864
unordered_multiset	5816	0	0	5816
unordered_set	5432	0	0	5432
vector	456	0	8	464
weak_ptr	624	0	8	632

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.