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 *nptr, char **endptr, int base);
12 long long strtoll(const char *nptr, char **endptr, int base);
14 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
16 strtoll():
18 _ISOC99_SOURCE
19 || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
20
22 The strtol() function converts the initial part of the string in nptr
23 to a long integer value according to the given base, which must be be‐
24 tween 2 and 36 inclusive, or be the special value 0.
25 The string may begin with an arbitrary amount of white space (as deter‐
27 mined by isspace(3)) followed by a single optional '+' or '-' sign. If
28 base is zero or 16, the string may then include a "0x" or "0X" prefix,
29 and the number will be read in base 16; otherwise, a zero base is taken
30 as 10 (decimal) unless the next character is '0', in which case it is
31 taken as 8 (octal).
32 The remainder of the string is converted to a long value in the obvious
34 manner, stopping at the first character which is not a valid digit in
35 the given base. (In bases above 10, the letter 'A' in either uppercase
36 or lowercase represents 10, 'B' represents 11, and so forth, with 'Z'
37 representing 35.)
38 If endptr is not NULL, strtol() stores the address of the first invalid
40 character in *endptr. If there were no digits at all, strtol() stores
41 the original value of nptr in *endptr (and returns 0). In particular,
42 if *nptr is not '\0' but **endptr is '\0' on return, the entire string
43 is valid.
44 The strtoll() function works just like the strtol() function but re‐
46 turns a long long integer value.
47
49 The strtol() function returns the result of the conversion, unless the
50 value would underflow or overflow. If an underflow occurs, strtol()
51 returns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX.
52 In both cases, errno is set to ERANGE. Precisely the same holds for
53 strtoll() (with LLONG_MIN and LLONG_MAX instead of LONG_MIN and
54 LONG_MAX).
55
57 EINVAL (not in C99) The given base contains an unsupported value.
58 ERANGE The resulting value was out of range.
60 The implementation may also set errno to EINVAL in case no conversion
62 was performed (no digits seen, and 0 returned).
63
65 For an explanation of the terms used in this section, see at‐
66 tributes(7).
67 ┌──────────────────────────────┬───────────────┬────────────────┐
69 │Interface │ Attribute │ Value │
70 ├──────────────────────────────┼───────────────┼────────────────┤
71 │strtol(), strtoll(), strtoq() │ Thread safety │ MT-Safe locale │
72 └──────────────────────────────┴───────────────┴────────────────┘
74 strtol(): POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4, 4.3BSD.
75 strtoll(): POSIX.1-2001, POSIX.1-2008, C99.
77
79 Since strtol() can legitimately return 0, LONG_MAX, or LONG_MIN
80 (LLONG_MAX or LLONG_MIN for strtoll()) on both success and failure, the
81 calling program should set errno to 0 before the call, and then deter‐
82 mine if an error occurred by checking whether errno has a nonzero value
83 after the call.
84 According to POSIX.1, in locales other than "C" and "POSIX", these
86 functions may accept other, implementation-defined numeric strings.
87 BSD also has
89 quad_t strtoq(const char *nptr, char **endptr, int base);
91 with completely analogous definition. Depending on the wordsize of the
93 current architecture, this may be equivalent to strtoll() or to str‐
94 tol().
95
97 The program shown below demonstrates the use of strtol(). The first
98 command-line argument specifies a string from which strtol() should
99 parse a number. The second (optional) argument specifies the base to
100 be used for the conversion. (This argument is converted to numeric
101 form using atoi(3), a function that performs no error checking and has
102 a simpler interface than strtol().) Some examples of the results pro‐
103 duced by this program are the following:
104 $ ./a.out 123
106 strtol() returned 123
107 $ ./a.out ' 123'
108 strtol() returned 123
109 $ ./a.out 123abc
110 strtol() returned 123
111 Further characters after number: "abc"
112 $ ./a.out 123abc 55
113 strtol: Invalid argument
114 $ ./a.out ''
115 No digits were found
116 $ ./a.out 4000000000
117 strtol: Numerical result out of range
118 Program source
120 #include <stdlib.h>
122 #include <limits.h>
123 #include <stdio.h>
124 #include <errno.h>
125 int
127 main(int argc, char *argv[])
128 {
129 int base;
130 char *endptr, *str;
131 long val;
132 if (argc < 2) {
134 fprintf(stderr, "Usage: %s str [base]\n", argv[0]);
135 exit(EXIT_FAILURE);
136 }
137 str = argv[1];
139 base = (argc > 2) ? atoi(argv[2]) : 0;
140 errno = 0; /* To distinguish success/failure after call */
142 val = strtol(str, &endptr, base);
143 /* Check for various possible errors */
145 if (errno != 0) {
147 perror("strtol");
148 exit(EXIT_FAILURE);
149 }
150 if (endptr == str) {
152 fprintf(stderr, "No digits were found\n");
153 exit(EXIT_FAILURE);
154 }
155 /* If we got here, strtol() successfully parsed a number */
157 printf("strtol() returned %ld\n", val);
159 if (*endptr != '\0') /* Not necessarily an error... */
161 printf("Further characters after number: \"%s\"\n", endptr);
162 exit(EXIT_SUCCESS);
164 }
165
167 atof(3), atoi(3), atol(3), strtod(3), strtoimax(3), strtoul(3),
168
170 This page is part of release 5.10 of the Linux man-pages project. A
171 description of the project, information about reporting bugs, and the
172 latest version of this page, can be found at
173 https://www.kernel.org/doc/man-pages/.
174GNU 2020-11-01 STRTOL(3)