Disabling iostream

For embedded or freestanding builds where <iostream> is unwanted, units can be compiled without it. Define UNIT_LIB_DISABLE_IOSTREAM before including the library. The unit types, arithmetic, conversions, and name()/abbreviation() all continue to work; only the stream/string rendering is removed.

What it does

Defining the macro drops the operator<< overloads, to_string, and the <clocale>/<iostream> includes. Everything else is unaffected.

#define UNIT_LIB_DISABLE_IOSTREAM
#include <units/length.h>
 
int main()
{
    using namespace units;
    using namespace units::literals;
 
    meters d = 5.0_m;
    double v = d.value();          // works
    const char* a = d.abbreviation();  // "m" — still available (it is a plain const char*)
    // std::cout << d;             // NOT available in this mode
    (void)v; (void)a;
}

name() and abbreviation() return const char* and do not depend on <iostream> or <string>, so they remain available for producing a label without pulling in the streaming machinery.

How to set it

Per translation unit — define the macro before the first units include:

#define UNIT_LIB_DISABLE_IOSTREAM
#include <units.h>

Project-wide via CMake — set the UNITS_DISABLE_IOSTREAM option, which defines the macro on the interface target for every consumer:

set(UNITS_DISABLE_IOSTREAM ON)
add_subdirectory(units)
target_link_libraries(myapp PRIVATE units::units)

Note — embedded builds. On platforms whose system headers define macros that clash with the SI abbreviations, also see the macro-clash guidance (#undef pascal on Windows; several single-letter #undefs on some ARM toolchains). Disabling iostream is commonly combined with those on embedded targets. The related configuration macros are listed in configuration.