将字符串转换成长整型数
相关函数atof，atoi，atol，strtod，strtoul
表头文件 #include <stdlib.h> 定义函数 long int strtol(const char *nptr, char **endptr, int base); 函数说明strtol()会将参数nptr字符串根据参数base来转换成长整型数。参数base范围从2至36，或0。参数base代表采用的进制方式，如base值为10则采用10进制，若base值为16则采用16进制等。当base值为0时则是采用10进制做转换，但遇到如'0x'前置字符则会使用16进制做转换。一开始strtol()会扫描参数nptr字符串，跳过前面的空格字符，直到遇上数字或正负符号才开始做转换，再遇到非数字或字符串结束时(' ')结束转换，并将结果返回。若参数endptr不为NULL，则会将遇到不合条件而终止的nptr中的字符指针由endptr返回。
返回值返回转换后的长整型数，否则返回ERANGE并将错误代码存入errno中。
附加说明ERANGE指定的转换字符串超出合法范围。
fddbq /* 将字符串a，b，c 分别采用10，2，16进制转换成数字*/#include <stdlib.h>#include <stdio.h>int main(){ char a[] = "10000000000"; char b[] = "10000000000"; char c[] = "ffff"; printf("a = %ldn",strtol(a,NULL,10)); printf("b = %ldn",strtol(b,NULL,2)); printf("c = %ldn",strtol(c,NULL,16)); return 0;} 执行 a = 10000000000b = 1024c = 65535 man STRTOL(3) Linux Programmer's Manual STRTOL(3)NAME strtol, strtoll, strtoq - convert a string to a long integerSYNOPSIS #include <stdlib.h> long int strtol(const char *nptr, char **endptr, int base); long long int strtoll(const char *nptr, char **endptr, int base); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): strtoll(): _XOPEN_SOURCE >= 600 || _BSD_SOURCE || _SVID_SOURCE || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99DESCRIPTION The strtol() function converts the initial part of the string in nptr to a long integer value accord‐ ing to the given base, which must be between 2 and 36 inclusive, or be the special value 0. The string may begin with an arbitrary amount of white space (as determined by isspace(3)) followed by a single optional '+' or '-' sign. If base is zero or 16, the string may then include a "0x" pre‐ fix, and the number will be read in base 16; otherwise, a zero base is taken as 10 (decimal) unless the next character is '0', in which case it is taken as 8 (octal). The remainder of the string is converted to a long int value in the obvious manner, stopping at the first character which is not a valid digit in the given base. (In bases above 10, the letter 'A' in either uppercase or lowercase represents 10, 'B' represents 11, and so forth, with 'Z' representing 35.) If endptr is not NULL, strtol() stores the address of the first invalid character in *endptr. If there were no digits at all, strtol() stores the original value of nptr in *endptr (and returns 0). In particular, if *nptr is not ' ' but **endptr is ' ' on return, the entire string is valid. The strtoll() function works just like the strtol() function but returns a long long integer value.RETURN VALUE The strtol() function returns the result of the conversion, unless the value would underflow or over‐ flow. If an underflow occurs, strtol() returns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX. In both cases, errno is set to ERANGE. Precisely the same holds for strtoll() (with LLONG_MIN and LLONG_MAX instead of LONG_MIN and LONG_MAX).ERRORS EINVAL (not in C99) The given base contains an unsupported value. ERANGE The resulting value was out of range. The implementation may also set errno to EINVAL in case no conversion was performed (no digits seen, and 0 returned).ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌──────────────────────────────┬───────────────┬────────────────┐ │Interface │ Attribute │ Value │ ├──────────────────────────────┼───────────────┼────────────────┤ │strtol(), strtoll(), strtoq() │ Thread safety │ MT-Safe locale │ └──────────────────────────────┴───────────────┴────────────────┘CONFORMING TO strtol(): POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4, 4.3BSD. strtoll(): POSIX.1-2001, POSIX.1-2008, C99.NOTES Since strtol() can legitimately return 0, LONG_MAX, or LONG_MIN (LLONG_MAX or LLONG_MIN for str‐ toll()) on both success and failure, the calling program should set errno to 0 before the call, and then determine if an error occurred by checking whether errno has a nonzero value after the call. According to POSIX.1, in locales other than the "C" and "POSIX", these functions may accept other, implementation-defined numeric strings. BSD also has quad_t strtoq(const char *nptr, char **endptr, int base); with completely analogous definition. Depending on the wordsize of the current architecture, this may be equivalent to strtoll() or to strtol().EXAMPLE The program shown below demonstrates the use of strtol(). The first command-line argument specifies a string from which strtol() should parse a number. The second (optional) argument specifies the base to be used for the conversion. (This argument is converted to numeric form using atoi(3), a function that performs no error checking and has a simpler interface than strtol().) Some examples of the results produced by this program are the following: $ ./a.out 123 strtol() returned 123 $ ./a.out ' 123' strtol() returned 123 $ ./a.out 123abc strtol() returned 123 Further characters after number: abc $ ./a.out 123abc 55 strtol: Invalid argument $ ./a.out '' No digits were found $ ./a.out 4000000000 strtol: Numerical result out of range Program source #include <stdlib.h> #include <limits.h> #include <stdio.h> #include <errno.h> int main(int argc, char *argv[]) { int base; char *endptr, *str; long val; if (argc < 2) { fprintf(stderr, "Usage: %s str [base]n", argv[0]); exit(EXIT_FAILURE); } str = argv[1]; base = (argc > 2) ? atoi(argv[2]) : 10; errno = 0; /* To distinguish success/failure after call */ val = strtol(str, &endptr, base); /* Check for various possible errors */ if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN)) || (errno != 0 && val == 0)) { perror("strtol"); exit(EXIT_FAILURE); } if (endptr == str) { fprintf(stderr, "No digits were foundn"); exit(EXIT_FAILURE); } /* If we got here, strtol() successfully parsed a number */ printf("strtol() returned %ldn", val); if (*endptr != ' ') /* Not necessarily an error... */ printf("Further characters after number: %sn", endptr); exit(EXIT_SUCCESS); }SEE ALSO atof(3), atoi(3), atol(3), strtod(3), strtoul(3)COLOPHON This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.GNU 2015-08-08 STRTOL(3)