关于一个很烦的函数strtoul

感觉strtoul这个函数很烦
主要是在对返回值的检查上
网上有一个例子
#include
#include
#include
#include
#define LENGTH 40

main()
{
    char String[LENGTH], *endptr;
    long int    retval;

    (void)setlocale(LC_ALL, "");
    if (fgets(String, LENGTH, stdin) != NULL) {
        errno = 0;

        retval = strtol ( String, &endptr, 0 );

        if (retval == 0 && (errno != 0
                    || String == endptr)) {
            /* No conversion could be performed */
            printf("No conversion performed\n");
        } else if (errno !=0 && (retval == LONG_MAX
                     || retval == LONG_MIN)) {
            /* Error handling */
        } else {
            /* retval contains long integer */
            printf("Integer in decimal is %d\n", retval);
        }
    }
}

The strtoul() function shall not change the setting of errno if successful.

Since 0, {ULONG_MAX}, and {ULLONG_MAX} are returned on error and are also valid returns on success, an application  wishing  to  check  for error situations should set errno to 0, then call strtoul() or strtoull(), then check errno.