C251 User's Guide
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C251 User's Guide

C251 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Error Messages Library Reference Library Files Source Code Standard Types jmp_buf va_list Macros CBYTE CVAR CARRAY DARRAY DBYTE DVAR HARRAY HBYTE HVAR NARRAY NBYTE NVAR XARRAY XBYTE XVAR Routines by Category Buffer Manipulation Routines Character Routines Data Conversion Routines Intrinsic Routines Math Routines Memory Allocation Routines Stream I/O Routines String Routines Variable Length Argument Routines Miscellaneous Routines Include Files SFR Definitions absacc.h assert.h ctype.h float.h intrins.h limits.h math.h setjmp.h stdarg.h stddef.h stdio.h stdlib.h string.h Reference _chkdouble_ _chkfloat_ _crol_ _cror_ _getkey _irol_ _iror_ _lrol_ _lror_ _nop_ _testbit_ _tolower _toupper abs acos asin assert atan atan2 atof atoi atol cabs calloc ceil cos cosh exp fabs fcalloc ffree finit_mempool floor fmalloc fmemcpy fmemset frealloc free getchar gets hmemccpy hmemchr hmemcmp hmemcpy hmemmove hmemset hstrcmp hstrcpy hstrlen hstrncpy init_mempool isalnum isalpha iscntrl isdigit isgraph islower isprint ispunct isspace isupper isxdigit labs log log10 longjmp malloc memccpy memchr memcmp memcpy memmove memset modf offsetof pow printf putchar puts rand realloc scanf setjmp sin sinh sprintf sqrt srand sscanf strcat strchr strcmp strcpy strcspn strlen strncat strncmp strncpy strpbrk strpos strrchr strrpbrk strrpos strspn tan tanh toascii toint tolower toupper ungetchar va_arg va_end va_start vprintf vsprintf xcalloc xfree xinit_mempool xmalloc xmemcpy xmemset xrealloc Appendix

log

Summary
#include <math.h>

double log (
  double val);   /* value to take natural logarithm of */
Description

The log function calculates the natural logarithm for the floating-point number val. The logarithm is the exponent to which the base (e or 2.718282... in the case of natural logs) must be raised to equal val. Or,

loge ex = val

Return Value

The log function returns the floating-point natural logarithm of val.

  • If x < 0, log returns NaN.
  • If x = 0, log returns -INF.
See Also

exp, log10

Example
#include <math.h>
#include <stdio.h> /* for printf */

void tst_log (void) {
  float x;
  float y;

  x = 2.718282;
  x *= x;

  y = log (x); /* y = 2 */

  printf ("LOG(%f) = %f\n", x, y);
}
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