Converts a double number to a string. This is a version of _ecvt with security enhancements as described in Security Features in the CRT.


errno_t _ecvt_s(
   char * _Buffer,
   size_t _SizeInBytes,
   double _Value,
   int _Count,
   int *_Dec,
   int *_Sign
template <size_t size>
errno_t _ecvt_s(
   char (&_Buffer)[size],
   double _Value,
   int _Count,
   int *_Dec,
   int *_Sign
); // C++ only


Filled with the pointer to the string of digits, the result of the conversion.

Size of the buffer in bytes.

Number to be converted.

Number of digits stored.

Stored decimal-point position.

Sign of the converted number.

Return Value

Zero if successful. The return value is an error code if there is a failure. Error codes are defined in Errno.h. For more information, see errno, _doserrno, _sys_errlist, and _sys_nerr.

In the case of an invalid parameter, as listed in the following table, this function invokes the invalid parameter handler, as described in Parameter Validation. If execution is allowed to continue, this function sets errno to EINVAL and returns EINVAL.

Error Conditions

_Buffer _SizeInBytes _Value _Count _Dec _Sign Return value Value in buffer
NULL any any any any any EINVAL Not modified.
Not NULL (points to valid memory) <=0 any any any any EINVAL Not modified.
any any any any NULL any EINVAL Not modified.
any any any any any NULL EINVAL Not modified.

Security Issues

_ecvt_s might generate an access violation if buffer does not point to valid memory and is not NULL.


The _ecvt_s function converts a floating-point number to a character string. The _Value parameter is the floating-point number to be converted. This function stores up to count digits of _Value as a string and appends a null character ('\0'). If the number of digits in _Value exceeds _Count, the low-order digit is rounded. If there are fewer than count digits, the string is padded with zeros.

Only digits are stored in the string. The position of the decimal point and the sign of _Value can be obtained from _Dec and _Sign after the call. The _Dec parameter points to an integer value giving the position of the decimal point with respect to the beginning of the string. A 0 or negative integer value indicates that the decimal point lies to the left of the first digit. The _Sign parameter points to an integer that indicates the sign of the converted number. If the integer value is 0, the number is positive. Otherwise, the number is negative.

A buffer of length _CVTBUFSIZE is sufficient for any floating-point value.

The difference between _ecvt_s and _fcvt_s is in the interpretation of the _Count parameter. _ecvt_s interprets _Count as the total number of digits in the output string, whereas _fcvt_s interprets _Count as the number of digits after the decimal point.

In C++, using this function is simplified by a template overload; the overload can infer buffer length automatically, eliminating the need to specify a size argument. For more information, see Secure Template Overloads.

The debug version of this function first fills the buffer with 0xFE. To disable this behavior, use _CrtSetDebugFillThreshold.

By default, this function's global state is scoped to the application. To change this, see Global state in the CRT.


Function Required header Optional header
_ecvt_s <stdlib.h> <errno.h>

For more compatibility information, see Compatibility.


// ecvt_s.c
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

int main( )
    char * buf = 0;
    int decimal;
    int sign;
    int err;

    buf = (char*) malloc(_CVTBUFSIZE);
    err = _ecvt_s(buf, _CVTBUFSIZE, 1.2, 5, &decimal, &sign);

    if (err != 0)
        printf("_ecvt_s failed with error code %d\n", err);

    printf("Converted value: %s\n", buf);
Converted value: 12000

See also

Data Conversion
Floating-Point Support
atof, _atof_l, _wtof, _wtof_l