系统数据文件和信息

#include <pwd.h>
#include <stddef.h>
#include <string.h>

struct passwd *getpwnam(const char *name) {
    struct passwd *ptr;
    setpwent();
    while ((ptr = getpwent()) != NULL) {
        //printf("%s\n", ptr->pw_name);
        if (strcmp(name, ptr->pw_name) == 0)
            break;
    }
    endpwent();
    return ptr;
}

int main() {
    if (getpwnam("root"))
        printf("find root");
    else
        printf("Not find root");
}

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void) {
    time_t t;
    struct tm *tmp;
    char buf1[16];
    char buf2[64];

    time(&t);
    tmp = localtime(&t);
    if (strftime(buf1, 16, "time and date: %r, %a %b %d, %Y", tmp) == 0)
        printf("buffer length 16 is too small\n");
    else
        printf("%s\n", buf1);
    if (strftime(buf2, 64, "time and date: %r, %a %b %d, %Y", tmp) == 0)
        printf("buffer length 64 is too small\n");
    else
        printf("%s\n", buf2);
    exit(0);
}