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The latest version of this topic can be found at _ecvt_s.

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  


[out] _Buffer
Filled with the pointer to the string of digits, the result of the conversion.

[in] _SizeInBytes
Size of the buffer in bytes.

[in] _Value
Number to be converted.

[in] _Count
Number of digits stored.

[out] _Dec
Stored decimal-point position.

[out] _Sign
Sign of the converted number.

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_SignReturn valueValue in buffer
NULLanyanyanyanyanyEINVALNot modified.
Not NULL (points to valid memory)<=0anyanyanyanyEINVALNot modified.
anyanyanyanyNULLanyEINVALNot modified.
anyanyanyanyanyNULLEINVALNot 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 0xFD. To disable this behavior, use _CrtSetDebugFillThreshold.

FunctionRequired headerOptional header

For more compatibility information, see Compatibility in the Introduction.

// 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  


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