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### 2.15 `ecvtbuf`, `fcvtbuf`—double or float to string

Synopsis

    #include <stdio.h>

    char *ecvtbuf(double val, int chars, int *decpt,
        int *sgn, char *buf);

    char *fcvtbuf(double val, int decimals, int *decpt,
        int *sgn, char *buf);

Description
`ecvtbuf` and `fcvtbuf` produce (null-terminated) strings of digits representating the `double` number val.

The only difference between `ecvtbuf` and `fcvtbuf` is the interpretation of the second argument (chars or decimals). For `ecvtbuf`, the second argument chars specifies the total number of characters to write (which is also the number of significant digits in the formatted string, since these two functions write only digits). For `fcvtbuf`, the second argument decimals specifies the number of characters to write after the decimal point; all digits for the integer part of val are always included.

Since `ecvtbuf` and `fcvtbuf` write only digits in the output string, they record the location of the decimal point in `*decpt`, and the sign of the number in `*sgn`. After formatting a number, `*decpt` contains the number of digits to the left of the decimal point. `*sgn` contains `0` if the number is positive, and `1` if it is negative. For both functions, you supply a pointer buf to an area of memory to hold the converted string.

Returns
Both functions return a pointer to buf, the string containing a character representation of val.

Portability
Neither function is ANSI C.

Supporting OS subroutines required: `close`, `fstat`, `isatty`, `lseek`, `read`, `sbrk`, `write`.