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Convert double to ASCII string
+ View other versions (4)


#include <stdlib.h>
char ecvt (double value, int ndigit, int * restrict decpt, int * restrict sign)
char fcvt (double value, int ndigit, int * restrict decpt, int * restrict sign)
char gcvt (double value, int ndigit, char *buf)


These functions are provided for compatibility with legacy code. New code should use the function for improved safety and portability.

The ecvt, fcvt and gcvt functions convert the double precision floating-point number value to a NUL-terminated ASCII string.

The ecvt function converts value to a NUL-terminated string of exactly ndigit digits and returns a pointer to that string. The result is padded with zeroes from left to right as needed. There are no leading zeroes unless value itself is 0. The least significant digit is rounded in an implementation-dependent manner. The position of the decimal point relative to the beginning of the string is stored in decpt. A negative value indicates that the decimal point is located to the left of the returned digits (this occurs when there is no whole number component to value). If value is zero, it is unspecified whether the integer pointed to by decpt will be 0 or 1. The decimal point itself is not included in the returned string. If the sign of the result is negative, the integer pointed to by sign is non-zero; otherwise, it is 0.

If the converted value is out of range or is not representable, the contents of the returned string are unspecified.

The fcvt function is identical to ecvt with the exception that ndigit specifies the number of digits after the decimal point (zero-padded as needed).

The gcvt function converts value to a NULL-terminated string similar to the reference:printf format specifier and stores the result in buf. It produces ndigit significant digits similar to the reference:printf format specifier where possible. If ndigit does allow sufficient precision, the result is stored in exponential notation similar to the reference:printf format specifier. If value is less than zero, buf will be prefixed with a minus sign. A decimal point is included in the returned string if value is not a whole number. Unlike the ecvt and fcvt functions, buf is not zero-padded.

Example 1

#include <stdio.h>
#include <stdlib.h>
int main()
  int decimal, sign;  
  char *buffer = ecvt(3.1415926535, 11, &decimal, &sign);
  printf("pi = %c.%s\n", buffer[0], buffer + 1);
  return 0;

pi = 3.1415926535

Return Values

The ecvt, fcvt and gcvt functions return a NUL-terminated string representation of value.


The ecvt and fcvt functions return a pointer to internal storage space that will be overwritten by subsequent calls to either function.

The maximum possible precision of the return value is limited by the precision of a double and may not be the same on all architectures.

The function is preferred over these functions for new code.