#176 Limits
Numeric limits information available in the C standard library (and finding another clang/gcc difference).
Notes
Since C runs on many computer architectures, numeric limits can vary. The standard library provides support for checking numeric limits at runtime.
Running the Example
See example.c for details. A makefile compiles and runs:
$ make
gcc-10 -Wall -O0 -std=c11 example.c -o example
./example
## Limits of library types:
PTRDIFF_MIN = -9223372036854775808
PTRDIFF_MAX = +9223372036854775807
SIZE_MAX = 18446744073709551615
SIG_ATOMIC_MIN = -2147483648
SIG_ATOMIC_MAX = +2147483647
WCHAR_MIN = -2147483648
WCHAR_MAX = +2147483647
WINT_MIN = -2147483648
WINT_MAX = 2147483647
## Limits of integer types:
CHAR_BIT = 8
MB_LEN_MAX = 6
CHAR_MIN = -128
CHAR_MAX = +127
SCHAR_MIN = -128
SCHAR_MAX = +127
UCHAR_MAX = 255
SHRT_MIN = -32768
SHRT_MAX = +32767
USHRT_MAX = 65535
INT_MIN = -2147483648
INT_MAX = +2147483647
UINT_MAX = 4294967295
LONG_MIN = -9223372036854775808
LONG_MAX = +9223372036854775807
ULONG_MAX = 18446744073709551615
LLONG_MIN = -9223372036854775808
LLONG_MAX = +9223372036854775807
ULLONG_MAX = 18446744073709551615
## Limits of floating point types:
FLT_RADIX = 2
DECIMAL_DIG = 21
FLT_MIN = 1.175494e-38
FLT_MAX = 3.402823e+38
FLT_EPSILON = 1.192093e-07
FLT_DIG = 6
FLT_MANT_DIG = 24
FLT_MIN_EXP = -125
FLT_MIN_10_EXP = -37
FLT_MAX_EXP = 128
FLT_MAX_10_EXP = 38
FLT_ROUNDS = 1
FLT_EVAL_METHOD = 0
FLT_HAS_SUBNORM = 1
Limitations
I just discovered that the clang 10.0.0 headers don’t include the fix for *_HAS_SUBNORM floating point limits.
So to run the example above on my Mac, I’m using gcc-10 installed with brew:
$ gcc-10 -v
Using built-in specs.
COLLECT_GCC=gcc-10
COLLECT_LTO_WRAPPER=/usr/local/Cellar/gcc/10.2.0/libexec/gcc/x86_64-apple-darwin17/10.2.0/lto-wrapper
Target: x86_64-apple-darwin17
Configured with: ../configure --build=x86_64-apple-darwin17 --prefix=/usr/local/Cellar/gcc/10.2.0 --libdir=/usr/local/Cellar/gcc/10.2.0/lib/gcc/10 --disable-nls --enable-checking=release --enable-languages=c,c++,objc,obj-c++,fortran --program-suffix=-10 --with-gmp=/usr/local/opt/gmp --with-mpfr=/usr/local/opt/mpfr --with-mpc=/usr/local/opt/libmpc --with-isl=/usr/local/opt/isl --with-system-zlib --with-pkgversion='Homebrew GCC 10.2.0' --with-bugurl=https://github.com/Homebrew/homebrew-core/issues --disable-multilib SED=/usr/bin/sed
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.2.0 (Homebrew GCC 10.2.0)
Rather than the default gcc installed with Xcode:
$ gcc -v
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 10.0.0 (clang-1000.11.45.5)
Target: x86_64-apple-darwin17.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin