1strtol(3) Library Functions Manual strtol(3)
2
6 strtol, strtoll, strtoq - convert a string to a long integer
7
9 Standard C library (libc, -lc)
10
12 #include <stdlib.h>
13 long strtol(const char *restrict nptr,
15 char **restrict endptr, int base);
16 long long strtoll(const char *restrict nptr,
17 char **restrict endptr, int base);
18 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
20 strtoll():
22 _ISOC99_SOURCE
23 || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
24
26 The strtol() function converts the initial part of the string in nptr
27 to a long integer value according to the given base, which must be be‐
28 tween 2 and 36 inclusive, or be the special value 0.
29 The string may begin with an arbitrary amount of white space (as deter‐
31 mined by isspace(3)) followed by a single optional '+' or '-' sign. If
32 base is zero or 16, the string may then include a "0x" or "0X" prefix,
33 and the number will be read in base 16; otherwise, a zero base is taken
34 as 10 (decimal) unless the next character is '0', in which case it is
35 taken as 8 (octal).
36 The remainder of the string is converted to a long value in the obvious
38 manner, stopping at the first character which is not a valid digit in
39 the given base. (In bases above 10, the letter 'A' in either uppercase
40 or lowercase represents 10, 'B' represents 11, and so forth, with 'Z'
41 representing 35.)
42 If endptr is not NULL, strtol() stores the address of the first invalid
44 character in *endptr. If there were no digits at all, strtol() stores
45 the original value of nptr in *endptr (and returns 0). In particular,
46 if *nptr is not '\0' but **endptr is '\0' on return, the entire string
47 is valid.
48 The strtoll() function works just like the strtol() function but re‐
50 turns a long long integer value.
51
53 The strtol() function returns the result of the conversion, unless the
54 value would underflow or overflow. If an underflow occurs, strtol()
55 returns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX.
56 In both cases, errno is set to ERANGE. Precisely the same holds for
57 strtoll() (with LLONG_MIN and LLONG_MAX instead of LONG_MIN and
58 LONG_MAX).
59
61 EINVAL (not in C99) The given base contains an unsupported value.
62 ERANGE The resulting value was out of range.
64 The implementation may also set errno to EINVAL in case no conversion
66 was performed (no digits seen, and 0 returned).
67
69 For an explanation of the terms used in this section, see at‐
70 tributes(7).
71 ┌─────────────────────────────────────┬───────────────┬────────────────┐
73 │Interface │ Attribute │ Value │
74 ├─────────────────────────────────────┼───────────────┼────────────────┤
75 │strtol(), strtoll(), strtoq() │ Thread safety │ MT-Safe locale │
76 └─────────────────────────────────────┴───────────────┴────────────────┘
77
79 C11, POSIX.1-2008.
80
82 strtol()
83 POSIX.1-2001, C89, SVr4, 4.3BSD.
84 strtoll()
86 POSIX.1-2001, C99.
87
89 Since strtol() can legitimately return 0, LONG_MAX, or LONG_MIN
90 (LLONG_MAX or LLONG_MIN for strtoll()) on both success and failure, the
91 calling program should set errno to 0 before the call, and then deter‐
92 mine if an error occurred by checking whether errno has a nonzero value
93 after the call.
94 According to POSIX.1, in locales other than "C" and "POSIX", these
96 functions may accept other, implementation-defined numeric strings.
97 BSD also has
99 quad_t strtoq(const char *nptr, char **endptr, int base);
101 with completely analogous definition. Depending on the wordsize of the
103 current architecture, this may be equivalent to strtoll() or to str‐
104 tol().
105
107 The program shown below demonstrates the use of strtol(). The first
108 command-line argument specifies a string from which strtol() should
109 parse a number. The second (optional) argument specifies the base to
110 be used for the conversion. (This argument is converted to numeric
111 form using atoi(3), a function that performs no error checking and has
112 a simpler interface than strtol().) Some examples of the results pro‐
113 duced by this program are the following:
114 $ ./a.out 123
116 strtol() returned 123
117 $ ./a.out ' 123'
118 strtol() returned 123
119 $ ./a.out 123abc
120 strtol() returned 123
121 Further characters after number: "abc"
122 $ ./a.out 123abc 55
123 strtol: Invalid argument
124 $ ./a.out ''
125 No digits were found
126 $ ./a.out 4000000000
127 strtol: Numerical result out of range
128 Program source
130 #include <errno.h>
132 #include <limits.h>
133 #include <stdio.h>
134 #include <stdlib.h>
135 int
137 main(int argc, char *argv[])
138 {
139 int base;
140 char *endptr, *str;
141 long val;
142 if (argc < 2) {
144 fprintf(stderr, "Usage: %s str [base]\n", argv[0]);
145 exit(EXIT_FAILURE);
146 }
147 str = argv[1];
149 base = (argc > 2) ? atoi(argv[2]) : 0;
150 errno = 0; /* To distinguish success/failure after call */
152 val = strtol(str, &endptr, base);
153 /* Check for various possible errors. */
155 if (errno != 0) {
157 perror("strtol");
158 exit(EXIT_FAILURE);
159 }
160 if (endptr == str) {
162 fprintf(stderr, "No digits were found\n");
163 exit(EXIT_FAILURE);
164 }
165 /* If we got here, strtol() successfully parsed a number. */
167 printf("strtol() returned %ld\n", val);
169 if (*endptr != '\0') /* Not necessarily an error... */
171 printf("Further characters after number: \"%s\"\n", endptr);
172 exit(EXIT_SUCCESS);
174 }
175
177 atof(3), atoi(3), atol(3), strtod(3), strtoimax(3), strtoul(3)
178Linux man-pages 6.04 2023-03-30 strtol(3)