GCVT(3) Linux Programmer's Manual GCVT(3)

gcvt - convert a floating-point number to a string

#include <stdlib.h>
char *gcvt(double number, int ndigit, char *buf);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.12:
(_XOPEN_SOURCE >= 500) ! (_POSIX_C_SOURCE >= 200112L)
    || /* Glibc since 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _SVID_SOURCE
Before glibc 2.12:

The gcvt() function converts number to a minimal length null-terminated ASCII string and stores the result in buf. It produces ndigit significant digits in either printf(3) F format or E format.

The gcvt() function returns the address of the string pointed to by buf.

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
gcvt () Thread safety MT-Safe

Marked as LEGACY in POSIX.1-2001. POSIX.1-2008 removes the specification of gcvt(), recommending the use of sprintf(3) instead (though snprintf(3) may be preferable).

ecvt(3), fcvt(3), sprintf(3)