GoKawiilC standard leaves strtod error detection non-portable across libc implementations
A blog post examines C17 section 7.25.2.6, which governs error handling for strtod, strtof, strtold and related string-to-float conversion functions. It explains that these functions' ability to report overflow or underflow via errno depends on the math_errhandling macro, and that on libraries like musl where MATH_ERRNO is not advertised, there is no standard-compliant way to detect these conversion errors. The author notes that Linux man pages for these functions omit this detail entirely.
GoKawiil's interpretation of the reporting above, not reported fact.
This gap means code relying on errno after calling strtod-family functions to catch overflow/underflow may work on glibc but silently fail to detect errors on musl or other libraries that don't set MATH_ERRNO, creating portability bugs that are hard to anticipate from documentation alone. The author's analysis suggests that developers writing cross-platform C code may need additional checks beyond what the standard or common man pages describe to reliably catch these conversion failures.
- C17 standard ties strtod-family error reporting to the math_errhandling macro, not a guaranteed errno setting.
- On libc implementations like musl that don't define MATH_ERRNO, there's no standard-compliant way to detect overflow/underflow in string-to-float conversions.
- Linux man pages for strtod, strtof and strtold do not document this portability limitation.
Source: sebsite.pw, 2026-10-10
Published there as: “No portable way to detect string-to-float conversion errors in standard C”
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