Implementation defined
Implementation-defined behavior is behavior for which a language standard permits an implementation to choose among specified alternatives and requires it to document its choice.
Modern C
Implementation-defined behavior is C behavior for which an implementation must choose and document one permitted alternative.
- How it is used
- Explains why C programs must not generalize platform-dependent type properties or arithmetic object representations.
- How deep it goes
- Demonstrates integer byte order and character-width assumptions, while deferring representation details for other base types.
- Examples
- Uses a union, hexadecimal integer 0xAABBCCDD, byte-printing code, and little-endian output as concrete examples.
- What you can do after
- Evaluate/understand which C type and representation observations are portable and which depend on the implementation.
Modern C, Third Edition
Implementation-defined behavior is behavior for which the C implementation chooses among permitted alternatives and documents its choice.
- How it is used
- Explains why C programs must account for compiler and platform choices when selecting types or performing conversions.
- How deep it goes
- Defines implementation-defined behavior and illustrates type ranges, char signedness, and invalid conversions without detailing compiler mechanisms.
- Examples
- Uses char signedness, equal int and long ranges, and conversion of UINT_MAX to a signed type.
- What you can do after
- Diagnose portability risks by identifying type and conversion behavior that varies among C implementations.
Read how Modern C, Third Edition explains implementation defined →
Related concepts
- endiannessconfigured by · Endianness is the convention that determines the order in which the bytes of a multibyte value are represented in memory or a serialized form.
- implicit conversionproduced by · Implicit conversion is an automatic change of a value from one type to another according to language rules, without an explicit conversion operation in the source code.
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