`_gcvt`

บทความ
12/02/2022

Converts a floating-point value to a string, which it stores in a buffer. A more secure version of this function is available; see _gcvt_s.

Syntax

char *_gcvt(
   double value,
   int digits,
   char *buffer
);

Parameters

value
Value to be converted.

digits
Number of significant digits stored.

buffer
Storage location for the result.

Return value

_gcvt returns a pointer to the string of digits.

Remarks

The _gcvt function converts a floating-point value to a character string (which includes a decimal point and a possible sign byte) and stores the string in buffer. The buffer should be large enough to accommodate the converted value plus a terminating null character, which is appended automatically. If a buffer size of digits + 1 is used, the function overwrites the end of the buffer. The overwrite happens because the converted string includes a decimal point and can also contain sign and exponent information. The function doesn't account for the overflow. _gcvt attempts to produce digits digits in decimal format. If it can't, it produces digits digits in exponential format. Trailing zeros might be suppressed in the conversion.

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

This function validates its parameters. If buffer is NULL, the invalid parameter handler is invoked, as described in Parameter validation. If execution is allowed to continue, this function sets errno to EINVAL and returns NULL.

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

Requirements

Routine	Required header
`_gcvt`	<stdlib.h>

For more compatibility information, see Compatibility.

Example

// crt_gcvt.c
// compile with: /W3
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main( void )
{
   char buffer[_CVTBUFSIZE];
   double value = -1234567890.123;
   printf( "The following numbers were converted by _gcvt(value,12,buffer):\n" );
   _gcvt( value, 12, buffer ); // C4996
   // Note: _gcvt is deprecated; consider using _gcvt_s instead
   printf( "buffer: '%s' (%d chars)\n", buffer, strlen(buffer) );
   value *= 10;
   _gcvt( value, 12, buffer ); // C4996
   printf( "buffer: '%s' (%d chars)\n", buffer, strlen(buffer) );
   value *= 10;
   _gcvt( value, 12, buffer ); // C4996
   printf( "buffer: '%s' (%d chars)\n", buffer, strlen(buffer) );
   value *= 10;
   _gcvt( value, 12, buffer ); // C4996
   printf( "buffer: '%s' (%d chars)\n", buffer, strlen(buffer) );

   printf( "\n" );
   value = -12.34567890123;
   _gcvt( value, 12, buffer ); // C4996
   printf( "buffer: '%s' (%d chars)\n", buffer, strlen(buffer) );
   value /= 10;
   _gcvt( value, 12, buffer ); // C4996
   printf( "buffer: '%s' (%d chars)\n", buffer, strlen(buffer) );
   value /= 10;
   _gcvt( value, 12, buffer ); // C4996
   printf( "buffer: '%s' (%d chars)\n", buffer, strlen(buffer) );
   value /= 10;
   _gcvt( value, 12, buffer ); // C4996
   printf( "buffer: '%s' (%d chars)\n", buffer, strlen(buffer) );
}

The following numbers were converted by _gcvt(value,12,buffer):
buffer: '-1234567890.12' (14 chars)
buffer: '-12345678901.2' (14 chars)
buffer: '-123456789012' (13 chars)
buffer: '-1.23456789012e+012' (19 chars)

buffer: '-12.3456789012' (14 chars)
buffer: '-1.23456789012' (14 chars)
buffer: '-0.123456789012' (15 chars)
buffer: '-1.23456789012e-002' (19 chars)

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