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  2015-08-08 "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 .sp
  38 .BI "long int strtol(const char *" nptr ", char **" endptr ", int " base );
  39 .sp
  40 .BI "long long int strtoll(const char *" nptr ", char **" endptr \
  41 ", int " base );
  42 .fi
  43 .sp
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .sp
  49 .ad l
  50 .BR strtoll ():
  51 .RS 4
  52 _XOPEN_SOURCE\ >=\ 600 || _BSD_SOURCE || _SVID_SOURCE || _ISOC99_SOURCE ||
  53 _POSIX_C_SOURCE\ >=\ 200112L;
  54 .br
  55 or
  56 .I cc\ -std=c99
  57 .RE
  58 .ad
  59 .SH DESCRIPTION
  60 The
  61 .BR strtol ()
  62 function converts the initial part of the string
  63 in
  64 .I nptr
  65 to a long integer value according to the given
  66 .IR base ,
  67 which must be between 2 and 36 inclusive, or be the special value 0.
  68 .PP
  69 The string may begin with an arbitrary amount of white space (as
  70 determined by
  71 .BR isspace (3))
  72 followed by a single optional \(aq+\(aq or \(aq\-\(aq sign.
  73 If
  74 .I base
  75 is zero or 16, the string may then include a
  76 "0x" prefix, and the number will be read in base 16; otherwise, a
  77 zero
  78 .I base
  79 is taken as 10 (decimal) unless the next character
  80 is \(aq0\(aq, in which case it is taken as 8 (octal).
  81 .PP
  82 The remainder of the string is converted to a
  83 .I long int
  84 value
  85 in the obvious manner, stopping at the first character which is not a
  86 valid digit in the given base.
  87 (In bases above 10, the letter \(aqA\(aq in
  88 either uppercase or lowercase represents 10, \(aqB\(aq represents 11, and so
  89 forth, with \(aqZ\(aq representing 35.)
  90 .PP
  91 If
  92 .I endptr
  93 is not NULL,
  94 .BR strtol ()
  95 stores the address of the
  96 first invalid character in
  97 .IR *endptr .
  98 If there were no digits at
  99 all,
 100 .BR strtol ()
 101 stores the original value of
 102 .I nptr
 103 in
 104 .I *endptr
 105 (and returns 0).
 106 In particular, if
 107 .I *nptr
 108 is not \(aq\\0\(aq but
 109 .I **endptr
 110 is \(aq\\0\(aq on return, the entire string is valid.
 111 .PP
 112 The
 113 .BR strtoll ()
 114 function works just like the
 115 .BR strtol ()
 116 function but returns a long long integer value.
 117 .SH RETURN VALUE
 118 The
 119 .BR strtol ()
 120 function returns the result of the conversion,
 121 unless the value would underflow or overflow.
 122 If an underflow occurs,
 123 .BR strtol ()
 124 returns
 125 .BR LONG_MIN .
 126 If an overflow occurs,
 127 .BR strtol ()
 128 returns
 129 .BR LONG_MAX .
 130 In both cases,
 131 .I errno
 132 is set to
 133 .BR ERANGE .
 134 Precisely the same holds for
 135 .BR strtoll ()
 136 (with
 137 .B LLONG_MIN
 138 and
 139 .B LLONG_MAX
 140 instead of
 141 .B LONG_MIN
 142 and
 143 .BR LONG_MAX ).
 144 .SH ERRORS
 145 .TP
 146 .B EINVAL
 147 (not in C99)
 148 The given
 149 .I base
 150 contains an unsupported value.
 151 .TP
 152 .B ERANGE
 153 The resulting value was out of range.
 154 .LP
 155 The implementation may also set
 156 .IR errno
 157 to
 158 .B EINVAL
 159 in case
 160 no conversion was performed (no digits seen, and 0 returned).
 161 .SH ATTRIBUTES
 162 For an explanation of the terms used in this section, see
 163 .BR attributes (7).
 164 .TS
 165 allbox;
 166 lbw29 lb lb
 167 l l l.
 168 Interface       Attribute       Value
 169 T{
 170 .BR strtol (),
 171 .BR strtoll (),
 172 .BR strtoq ()
 173 T}      Thread safety   MT-Safe locale
 174 .TE
 175 .SH CONFORMING TO
 176 .BR strtol ():
 177 POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4, 4.3BSD.
 178
 179 .BR strtoll ():
 180 POSIX.1-2001, POSIX.1-2008, C99.
 181 .SH NOTES
 182 Since
 183 .BR strtol ()
 184 can legitimately return 0,
 185 .BR LONG_MAX ,
 186 or
 187 .B LONG_MIN
 188 .RB ( LLONG_MAX
 189 or
 190 .B LLONG_MIN
 191 for
 192 .BR strtoll ())
 193 on both success and failure, the calling program should set
 194 .I errno
 195 to 0 before the call,
 196 and then determine if an error occurred by checking whether
 197 .I errno
 198 has a nonzero value after the call.
 199
 200 According to POSIX.1,
 201 in locales other than the "C" and "POSIX",
 202 these functions may accept other,
 203 implementation-defined numeric strings.
 204 .LP
 205 BSD also has
 206 .sp
 207 .in +4n
 208 .nf
 209 .BI "quad_t strtoq(const char *" nptr ", char **" endptr ", int " base );
 210 .sp
 211 .in
 212 .fi
 213 with completely analogous definition.
 214 Depending on the wordsize of the current architecture, this
 215 may be equivalent to
 216 .BR strtoll ()
 217 or to
 218 .BR strtol ().
 219 .SH EXAMPLE
 220 The program shown below demonstrates the use of
 221 .BR strtol ().
 222 The first command-line argument specifies a string from which
 223 .BR strtol ()
 224 should parse a number.
 225 The second (optional) argument specifies the base to be used for
 226 the conversion.
 227 (This argument is converted to numeric form using
 228 .BR atoi (3),
 229 a function that performs no error checking and
 230 has a simpler interface than
 231 .BR strtol ().)
 232 Some examples of the results produced by this program are the following:
 233 .in +4n
 234 .nf
 235
 236 .RB "$" " ./a.out 123"
 237 strtol() returned 123
 238 .RB "$" " ./a.out \(aq    123\(aq"
 239 strtol() returned 123
 240 .RB "$" " ./a.out 123abc"
 241 strtol() returned 123
 242 Further characters after number: abc
 243 .RB "$" " ./a.out 123abc 55"
 244 strtol: Invalid argument
 245 .RB "$" " ./a.out \(aq\(aq"
 246 No digits were found
 247 .RB "$" " ./a.out 4000000000"
 248 strtol: Numerical result out of range
 249 .fi
 250 .in
 251 .SS Program source
 252 \&
 253 .nf
 254 #include <stdlib.h>
 255 #include <limits.h>
 256 #include <stdio.h>
 257 #include <errno.h>
 258
 259 int
 260 main(int argc, char *argv[])
 261 {
 262     int base;
 263     char *endptr, *str;
 264     long val;
 265
 266     if (argc < 2) {
 267         fprintf(stderr, "Usage: %s str [base]\\n", argv[0]);
 268         exit(EXIT_FAILURE);
 269     }
 270
 271     str = argv[1];
 272     base = (argc > 2) ? atoi(argv[2]) : 10;
 273
 274     errno = 0;    /* To distinguish success/failure after call */
 275     val = strtol(str, &endptr, base);
 276
 277     /* Check for various possible errors */
 278
 279     if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN))
 280             || (errno != 0 && val == 0)) {
 281         perror("strtol");
 282         exit(EXIT_FAILURE);
 283     }
 284
 285     if (endptr == str) {
 286         fprintf(stderr, "No digits were found\\n");
 287         exit(EXIT_FAILURE);
 288     }
 289
 290     /* If we got here, strtol() successfully parsed a number */
 291
 292     printf("strtol() returned %ld\\n", val);
 293
 294     if (*endptr != \(aq\\0\(aq)        /* Not necessarily an error... */
 295         printf("Further characters after number: %s\\n", endptr);
 296
 297     exit(EXIT_SUCCESS);
 298 }
 299 .fi
 300 .SH SEE ALSO
 301 .BR atof (3),
 302 .BR atoi (3),
 303 .BR atol (3),
 304 .BR strtod (3),
 305 .BR strtoul (3)