1STRTOL(3) Linux Programmer's Manual STRTOL(3)
2
6 strtol, strtoll, strtoq - convert a string to a long integer
7
9 #include <stdlib.h>
10 long strtol(const char *restrict nptr,
12 char **restrict endptr, int base);
13 long long strtoll(const char *restrict nptr,
14 char **restrict endptr, int base);
15 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
17 strtoll():
19 _ISOC99_SOURCE
20 || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
21
23 The strtol() function converts the initial part of the string in nptr
24 to a long integer value according to the given base, which must be be‐
25 tween 2 and 36 inclusive, or be the special value 0.
26 The string may begin with an arbitrary amount of white space (as deter‐
28 mined by isspace(3)) followed by a single optional '+' or '-' sign. If
29 base is zero or 16, the string may then include a "0x" or "0X" prefix,
30 and the number will be read in base 16; otherwise, a zero base is taken
31 as 10 (decimal) unless the next character is '0', in which case it is
32 taken as 8 (octal).
33 The remainder of the string is converted to a long value in the obvious
35 manner, stopping at the first character which is not a valid digit in
36 the given base. (In bases above 10, the letter 'A' in either uppercase
37 or lowercase represents 10, 'B' represents 11, and so forth, with 'Z'
38 representing 35.)
39 If endptr is not NULL, strtol() stores the address of the first invalid
41 character in *endptr. If there were no digits at all, strtol() stores
42 the original value of nptr in *endptr (and returns 0). In particular,
43 if *nptr is not '\0' but **endptr is '\0' on return, the entire string
44 is valid.
45 The strtoll() function works just like the strtol() function but re‐
47 turns a long long integer value.
48
50 The strtol() function returns the result of the conversion, unless the
51 value would underflow or overflow. If an underflow occurs, strtol()
52 returns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX.
53 In both cases, errno is set to ERANGE. Precisely the same holds for
54 strtoll() (with LLONG_MIN and LLONG_MAX instead of LONG_MIN and
55 LONG_MAX).
56
58 EINVAL (not in C99) The given base contains an unsupported value.
59 ERANGE The resulting value was out of range.
61 The implementation may also set errno to EINVAL in case no conversion
63 was performed (no digits seen, and 0 returned).
64
66 For an explanation of the terms used in this section, see at‐
67 tributes(7).
68 ┌─────────────────────────────────────┬───────────────┬────────────────┐
70 │Interface │ Attribute │ Value │
71 ├─────────────────────────────────────┼───────────────┼────────────────┤
72 │strtol(), strtoll(), strtoq() │ Thread safety │ MT-Safe locale │
73 └─────────────────────────────────────┴───────────────┴────────────────┘
74
76 strtol(): POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4, 4.3BSD.
77 strtoll(): POSIX.1-2001, POSIX.1-2008, C99.
79
81 Since strtol() can legitimately return 0, LONG_MAX, or LONG_MIN
82 (LLONG_MAX or LLONG_MIN for strtoll()) on both success and failure, the
83 calling program should set errno to 0 before the call, and then deter‐
84 mine if an error occurred by checking whether errno has a nonzero value
85 after the call.
86 According to POSIX.1, in locales other than "C" and "POSIX", these
88 functions may accept other, implementation-defined numeric strings.
89 BSD also has
91 quad_t strtoq(const char *nptr, char **endptr, int base);
93 with completely analogous definition. Depending on the wordsize of the
95 current architecture, this may be equivalent to strtoll() or to str‐
96 tol().
97
99 The program shown below demonstrates the use of strtol(). The first
100 command-line argument specifies a string from which strtol() should
101 parse a number. The second (optional) argument specifies the base to
102 be used for the conversion. (This argument is converted to numeric
103 form using atoi(3), a function that performs no error checking and has
104 a simpler interface than strtol().) Some examples of the results pro‐
105 duced by this program are the following:
106 $ ./a.out 123
108 strtol() returned 123
109 $ ./a.out ' 123'
110 strtol() returned 123
111 $ ./a.out 123abc
112 strtol() returned 123
113 Further characters after number: "abc"
114 $ ./a.out 123abc 55
115 strtol: Invalid argument
116 $ ./a.out ''
117 No digits were found
118 $ ./a.out 4000000000
119 strtol: Numerical result out of range
120 Program source
122 #include <stdlib.h>
124 #include <limits.h>
125 #include <stdio.h>
126 #include <errno.h>
127 int
129 main(int argc, char *argv[])
130 {
131 int base;
132 char *endptr, *str;
133 long val;
134 if (argc < 2) {
136 fprintf(stderr, "Usage: %s str [base]\n", argv[0]);
137 exit(EXIT_FAILURE);
138 }
139 str = argv[1];
141 base = (argc > 2) ? atoi(argv[2]) : 0;
142 errno = 0; /* To distinguish success/failure after call */
144 val = strtol(str, &endptr, base);
145 /* Check for various possible errors. */
147 if (errno != 0) {
149 perror("strtol");
150 exit(EXIT_FAILURE);
151 }
152 if (endptr == str) {
154 fprintf(stderr, "No digits were found\n");
155 exit(EXIT_FAILURE);
156 }
157 /* If we got here, strtol() successfully parsed a number. */
159 printf("strtol() returned %ld\n", val);
161 if (*endptr != '\0') /* Not necessarily an error... */
163 printf("Further characters after number: \"%s\"\n", endptr);
164 exit(EXIT_SUCCESS);
166 }
167
169 atof(3), atoi(3), atol(3), strtod(3), strtoimax(3), strtoul(3),
170
172 This page is part of release 5.12 of the Linux man-pages project. A
173 description of the project, information about reporting bugs, and the
174 latest version of this page, can be found at
175 https://www.kernel.org/doc/man-pages/.
176GNU 2021-03-22 STRTOL(3)