5.7.1.17 Smart-io Option
The -msmart-io=level option in
conjunction with the IO format string conversion specifications detected in your program
control the feature set (hence size) of the library code that is linked in to perform
formatted IO through functions like printf. See 19.1 Smart IO Routines for more
information on how the smart IO feature operates.
| Level | Smart IO features; linked library |
|---|---|
| 0 | Disabled; Full-featured library (largest code size) |
| 1 | Enabled; Minimal-featured library (smallest code size) |
| 2 | Manual control; Integer-only library |
When the smart IO feature is disabled (-msmart-io=0), a full
implementation of the IO functions will be linked into your program. All features of the
IO library functions will be available, and these may consume a significant amount of
the available program and data memory on the target device.
The default setting is for smart IO to be enabled with a minimal feature set. This can be
made explicit by using either the -msmart-io=1 or
-msmart-io option. When thus enabled, the compiler will link in the
least complex variant of the IO library that implements all of the IO functionality
required by the program, based on the conversion specifications detected in the
program's IO function format strings. This can substantially reduce the memory
requirements of your program, especially if you can eliminate in your program the use of
floating-point features.
If the format string in a call to an IO function is not a string literal, the compiler will not be able to detect the exact usage of the IO function and a full-featured variant of the IO library will be linked into the program image, even with smart IO enabled.
These options should be used consistently across all program modules to ensure an optimal selection of the library routines included in the program image.