# Qualcomm Hexagon C++ Library Supplement

This section describes how to select the C++ library to use of the
two that are provided with the Hexagon Tools and the reasons for
selecting one library over the other.

## Usage Details

The C++ libraries are distributed with the Hexagon Tools for use in
writing C++ programs. The libraries are used to support C++ language
features. They also include the containers, file I/O, strings,
exceptions, smart pointers, and other features described by the C++
standard. Two different libraries are distributed with the Hexagon
Tools: libstdc++ and libc++.

### Using the C++ library

By default, hexagon-clang++ uses the C++03 standard and selects the
libstdc++ library for compilation and linkage. If the more recent
standards are specified, such as C++11 (std=c++11), C++14
(std=c++14), etc., hexagon-clang++ will select the libc++ library for
compilation and linkage.

You can use the stdlib=libc++ or stdlib=libstdc++ arguments with
hexagon-clang++ to select the appropriate standard library.

### Differences between libstdc++ and libc++

libstdc++ is the “historical” C++ library, and it supports only C++98
and C++03 language modes. It can be used with standalone mode to
write and debug C++ programs. This standalone mode is often used in
conjunction with the Hexagon simulator.
See *Hexagon Stand-alone Application User Guide* (80-N2040-22).

libc++ was introduced to support C++11 and beyond. libc++ requires
support in the form of OS include paths for headers and libraries.
This means that many programs built with libc++ won’t successfully
compile without explicit -I/path/to/os/include arguments, and they
won’t link without explicit arguments for the linker as well.

The libc++ standard library is distributed as two distinct libraries,
libc++ and libc++abi. When -stdlib=libc++ is used, the
compiler/linker is configured to resolve to each of those respective
includes/libraries. If you use the -nostdlib argument to disable the
automatic inclusion of libc++, you should know that the C++ code will
require linkage with both libc++ and libc++abi.

### Compiling with C++11

When compiling source files in C++11 mode, you must use libc++. You
must also provide the necessary include paths to find the QuRT
headers.

For example:

hexagon-clang++ -std=c++11 -I/path/to/qurt/install/variant/include/qube -I/path/to/qurt/install/variant/include/posix -I/path/to/qurt/install/variant/include/qurt -c -o new_program.o new_program.cpp
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### System configuration limitations

#### Simulator

Some library features include time/date referenced by the epoch
(“wall clock”) and interval times that can be used in delays (for example,
`std::this_thread::sleep`) or time- bounded waits (try\_lock\_for(),
wait\_for(), etc.). In a normal system, these are often driven by a
timer tick interrupt that elapses at a specified interval. When using
hexagon-sim with QuRT, these features depend on co-simulators
(“cosims”) used to model this external device. The qtimer cosim may
be necessary to simulate a real hHexagon processor. See the
section on cosimulation in *Hexagon Simulator System API User Guide*
(80-N2040-18) for details. See the qtimer cosim example included
with the Hexagon tools for an example of using the qtimer cosim. This
example is found in *<Hexagon\_tools>/Examples/cosims/qtimer\_test*.

#### Target

Note that QuRT won’t provide a real UTC reference, so wall clock
times won’t match other processors in the SoC or in the outside
world.

Last Published: Oct 06, 2026

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