> ## Documentation Index > Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt > Use this file to discover all available pages before exploring further. # C long double The `long double` type in C is a standard scalar floating-point data type designed to provide precision and range greater than or equal to that of a standard `double`. It represents the maximum floating-point precision natively supported by the compiler and the target hardware architecture. ## Memory Representation and Precision The C standard does not mandate a strict bit-width for `long double`, only requiring that its precision is at least that of `double`. Consequently, its memory footprint and IEEE 754 implementation are highly architecture- and compiler-dependent: * **x86/x86\_64 (GCC/Clang on Linux/macOS):** Typically implemented as an 80-bit extended-precision format. Due to memory alignment requirements, `sizeof(long double)` evaluates to 12 or 16 bytes, though only 10 bytes (80 bits) are used for the value. * **ARM64/AArch64:** Often implemented as a 128-bit quadruple-precision floating-point format (`sizeof(long double) == 16`). * **MSVC (Windows):** Implemented as a 64-bit standard double-precision format. On this compiler, `long double` is strictly identical to `double` (`sizeof(long double) == 8`). ## Syntax and Literals By default, floating-point literals in C are of type `double`. To explicitly declare a `long double` literal, you must append the `L` or `l` suffix. Omitting the suffix causes the compiler to truncate the literal to `double` precision before assigning it to the `long double` variable. ```c theme={"dark"} // Correct: The 'L' suffix ensures the literal is treated as long double long double precise_val = 3.14159265358979323846264338327950288L; // Incorrect: Literal is truncated to double precision before assignment long double truncated_val = 3.14159265358979323846264338327950288; ``` ## Formatted Input/Output When interfacing with standard I/O functions (`printf`, `scanf`), `long double` requires the `L` length modifier combined with a floating-point conversion specifier (`f`, `e`, `g`, `a`). ```c theme={"dark"} #include int main(void) { long double num; // Input requires %Lf scanf("%Lf", &num); // Output requires %Lf (or %Le, %Lg). // .19 specifies 19 decimal places of precision. printf("%.19Lf\n", num); return 0; } ``` ## Standard Library Integration The C standard library provides dedicated functions and macros for `long double` operations to prevent implicit downcasting to `double`. **Math Functions (``)** Functions operating on `long double` are suffixed with `l`. ```c theme={"dark"} #include long double base = 2.0L; long double result = sqrtl(base); // Instead of sqrt() long double power = powl(base, 3.5L); // Instead of pow() ``` **Limits and Characteristics (``)** The `` header defines macros specific to `long double` (prefixed with `LDBL_`) that expose the implementation details of the type on the current architecture: * `LDBL_MANT_DIG`: Number of base-radix digits in the floating-point significand. * `LDBL_DIG`: Number of decimal digits that can be rounded and recovered without change. * `LDBL_MIN` / `LDBL_MAX`: Minimum normalized positive value and maximum representable finite value. * `LDBL_EPSILON`: The difference between 1.0 and the next representable `long double` value.

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