man3/strtol.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified Sun Jul 25 10:53:39 1993 by Rik Faith (faith@cs.unc.edu)
  30 .\" Added correction due to nsd@bbc.com (Nick Duffek) - aeb, 950610
  31 .TH STRTOL 3  2019-03-06 "GNU" "Linux Programmer's Manual"
  32 .SH NAME
  33 strtol, strtoll, strtoq \- convert a string to a long integer
  34 .SH SYNOPSIS
  35 .nf
  36 .B #include <stdlib.h>
  37 .PP
  38 .BI "long int strtol(const char *" nptr ", char **" endptr ", int " base );
  39 .PP
  40 .BI "long long int strtoll(const char *" nptr ", char **" endptr \
  41 ", int " base );
  42 .fi
  43 .PP
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .PP
  49 .ad l
  50 .BR strtoll ():
  51 .RS 4
  52 _ISOC99_SOURCE
  53     || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
  54 .RE
  55 .ad
  56 .SH DESCRIPTION
  57 The
  58 .BR strtol ()
  59 function converts the initial part of the string
  60 in
  61 .I nptr
  62 to a long integer value according to the given
  63 .IR base ,
  64 which must be between 2 and 36 inclusive, or be the special value 0.
  65 .PP
  66 The string may begin with an arbitrary amount of white space (as
  67 determined by
  68 .BR isspace (3))
  69 followed by a single optional \(aq+\(aq or \(aq\-\(aq sign.
  70 If
  71 .I base
  72 is zero or 16, the string may then include a
  73 "0x" or "0X" prefix, and the number will be read in base 16; otherwise, a
  74 zero
  75 .I base
  76 is taken as 10 (decimal) unless the next character
  77 is \(aq0\(aq, in which case it is taken as 8 (octal).
  78 .PP
  79 The remainder of the string is converted to a
  80 .I long int
  81 value
  82 in the obvious manner, stopping at the first character which is not a
  83 valid digit in the given base.
  84 (In bases above 10, the letter \(aqA\(aq in
  85 either uppercase or lowercase represents 10, \(aqB\(aq represents 11, and so
  86 forth, with \(aqZ\(aq representing 35.)
  87 .PP
  88 If
  89 .I endptr
  90 is not NULL,
  91 .BR strtol ()
  92 stores the address of the
  93 first invalid character in
  94 .IR *endptr .
  95 If there were no digits at
  96 all,
  97 .BR strtol ()
  98 stores the original value of
  99 .I nptr
 100 in
 101 .I *endptr
 102 (and returns 0).
 103 In particular, if
 104 .I *nptr
 105 is not \(aq\e0\(aq but
 106 .I **endptr
 107 is \(aq\e0\(aq on return, the entire string is valid.
 108 .PP
 109 The
 110 .BR strtoll ()
 111 function works just like the
 112 .BR strtol ()
 113 function but returns a long long integer value.
 114 .SH RETURN VALUE
 115 The
 116 .BR strtol ()
 117 function returns the result of the conversion,
 118 unless the value would underflow or overflow.
 119 If an underflow occurs,
 120 .BR strtol ()
 121 returns
 122 .BR LONG_MIN .
 123 If an overflow occurs,
 124 .BR strtol ()
 125 returns
 126 .BR LONG_MAX .
 127 In both cases,
 128 .I errno
 129 is set to
 130 .BR ERANGE .
 131 Precisely the same holds for
 132 .BR strtoll ()
 133 (with
 134 .B LLONG_MIN
 135 and
 136 .B LLONG_MAX
 137 instead of
 138 .B LONG_MIN
 139 and
 140 .BR LONG_MAX ).
 141 .SH ERRORS
 142 .TP
 143 .B EINVAL
 144 (not in C99)
 145 The given
 146 .I base
 147 contains an unsupported value.
 148 .TP
 149 .B ERANGE
 150 The resulting value was out of range.
 151 .PP
 152 The implementation may also set
 153 .IR errno
 154 to
 155 .B EINVAL
 156 in case
 157 no conversion was performed (no digits seen, and 0 returned).
 158 .SH ATTRIBUTES
 159 For an explanation of the terms used in this section, see
 160 .BR attributes (7).
 161 .TS
 162 allbox;
 163 lbw29 lb lb
 164 l l l.
 165 Interface       Attribute       Value
 166 T{
 167 .BR strtol (),
 168 .BR strtoll (),
 169 .BR strtoq ()
 170 T}      Thread safety   MT-Safe locale
 171 .TE
 172 .SH CONFORMING TO
 173 .BR strtol ():
 174 POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4, 4.3BSD.
 175 .PP
 176 .BR strtoll ():
 177 POSIX.1-2001, POSIX.1-2008, C99.
 178 .SH NOTES
 179 Since
 180 .BR strtol ()
 181 can legitimately return 0,
 182 .BR LONG_MAX ,
 183 or
 184 .B LONG_MIN
 185 .RB ( LLONG_MAX
 186 or
 187 .B LLONG_MIN
 188 for
 189 .BR strtoll ())
 190 on both success and failure, the calling program should set
 191 .I errno
 192 to 0 before the call,
 193 and then determine if an error occurred by checking whether
 194 .I errno
 195 has a nonzero value after the call.
 196 .PP
 197 According to POSIX.1,
 198 in locales other than the "C" and "POSIX",
 199 these functions may accept other,
 200 implementation-defined numeric strings.
 201 .PP
 202 BSD also has
 203 .PP
 204 .in +4n
 205 .EX
 206 .BI "quad_t strtoq(const char *" nptr ", char **" endptr ", int " base );
 207 .EE
 208 .in
 209 .PP
 210 with completely analogous definition.
 211 Depending on the wordsize of the current architecture, this
 212 may be equivalent to
 213 .BR strtoll ()
 214 or to
 215 .BR strtol ().
 216 .SH EXAMPLE
 217 The program shown below demonstrates the use of
 218 .BR strtol ().
 219 The first command-line argument specifies a string from which
 220 .BR strtol ()
 221 should parse a number.
 222 The second (optional) argument specifies the base to be used for
 223 the conversion.
 224 (This argument is converted to numeric form using
 225 .BR atoi (3),
 226 a function that performs no error checking and
 227 has a simpler interface than
 228 .BR strtol ().)
 229 Some examples of the results produced by this program are the following:
 230 .PP
 231 .in +4n
 232 .EX
 233 .RB "$" " ./a.out 123"
 234 strtol() returned 123
 235 .RB "$" " ./a.out \(aq    123\(aq"
 236 strtol() returned 123
 237 .RB "$" " ./a.out 123abc"
 238 strtol() returned 123
 239 Further characters after number: abc
 240 .RB "$" " ./a.out 123abc 55"
 241 strtol: Invalid argument
 242 .RB "$" " ./a.out \(aq\(aq"
 243 No digits were found
 244 .RB "$" " ./a.out 4000000000"
 245 strtol: Numerical result out of range
 246 .EE
 247 .in
 248 .SS Program source
 249 \&
 250 .EX
 251 #include <stdlib.h>
 252 #include <limits.h>
 253 #include <stdio.h>
 254 #include <errno.h>
 255
 256 int
 257 main(int argc, char *argv[])
 258 {
 259     int base;
 260     char *endptr, *str;
 261     long val;
 262
 263     if (argc < 2) {
 264         fprintf(stderr, "Usage: %s str [base]\en", argv[0]);
 265         exit(EXIT_FAILURE);
 266     }
 267
 268     str = argv[1];
 269     base = (argc > 2) ? atoi(argv[2]) : 10;
 270
 271     errno = 0;    /* To distinguish success/failure after call */
 272     val = strtol(str, &endptr, base);
 273
 274     /* Check for various possible errors */
 275
 276     if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN))
 277             || (errno != 0 && val == 0)) {
 278         perror("strtol");
 279         exit(EXIT_FAILURE);
 280     }
 281
 282     if (endptr == str) {
 283         fprintf(stderr, "No digits were found\en");
 284         exit(EXIT_FAILURE);
 285     }
 286
 287     /* If we got here, strtol() successfully parsed a number */
 288
 289     printf("strtol() returned %ld\en", val);
 290
 291     if (*endptr != \(aq\e0\(aq)        /* Not necessarily an error... */
 292         printf("Further characters after number: %s\en", endptr);
 293
 294     exit(EXIT_SUCCESS);
 295 }
 296 .EE
 297 .SH SEE ALSO
 298 .BR atof (3),
 299 .BR atoi (3),
 300 .BR atol (3),
 301 .BR strtod (3),
 302 .BR strtoul (3),
 303 .BR strtoimax (3)