8.1
运行下面代码，为什么输出会相同？
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| #include <stdio.h>
#include <unistd.h>
#include <pwd.h>
int main() {
struct passwd * p1 = getpwnam("redis");
struct passwd * p2 = getpwnam("sshd");
printf("getpwnam(\"redis\")->pw_uid = %u, getpwnam(\"sshd\")->pw_uid = %u\n", p1->pw_uid, p2->pw_uid);
printf("getpwnam(\"redis\") = %p, getpwnam(\"sshd\") = %p\n", p1, p2);
return 0;
}
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getpwnam和getpwuid返回的指针指向由静态分配的的内存，地址都是相同的，所以会导致相同。
8.2
用getpwent，setpwent，endpwent实现getpwnam
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| #include <stdio.h>
#include <pwd.h>
#include <string.h>
struct passwd getpwnamRet;
struct passwd *__getpwnam(const char *name) {
struct passwd *pwd = NULL;
while((pwd = getpwent()) != NULL) {
if(!strcmp(name, pwd->pw_name)) {
break;
}
}
endpwent();
if(pwd != NULL) {
memcpy(&getpwnamRet, pwd, sizeof(struct passwd));
return &getpwnamRet;
}
return NULL;
}
void printpwd(struct passwd *pwd) {
if(pwd == NULL) {
printf("User not Found!\n");
return;
}
printf("Login name:\t%s\n", pwd->pw_name);
printf("Login passwd:\t%s\n", pwd->pw_passwd);
printf("User uid:\t%u\n", pwd->pw_uid);
printf("User gid:\t%u\n", pwd->pw_gid);
printf("User info:\t%s\n", pwd->pw_gecos);
printf("Work dir:\t%s\n", pwd->pw_dir);
printf("Login shell:\t%s\n", pwd->pw_shell);
}
int main(int argc, char *argv[]) {
printpwd(__getpwnam(argv[1]));
return 0;
}
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事实上，没有必要为了定义全局变量getpwnamRet，因为getpwent的返回值本身就是静态区的
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| #include <stdio.h>
#include <pwd.h>
#include <string.h>
struct passwd *__getpwnam(const char *name) {
struct passwd *pwd = NULL;
while((pwd = getpwent()) != NULL) {
if(!strcmp(name, pwd->pw_name)) {
break;
}
}
endpwent();
return pwd;
}
void printpwd(struct passwd *pwd) {
if(pwd == NULL) {
printf("User not Found!\n");
return;
}
printf("Login name:\t%s\n", pwd->pw_name);
printf("Login passwd:\t%s\n", pwd->pw_passwd);
printf("User uid:\t%u\n", pwd->pw_uid);
printf("User gid:\t%u\n", pwd->pw_gid);
printf("User info:\t%s\n", pwd->pw_gecos);
printf("Work dir:\t%s\n", pwd->pw_dir);
printf("Login shell:\t%s\n", pwd->pw_shell);
}
int main(int argc, char *argv[]) {
struct passwd *p1 = __getpwnam(argv[1]), *p2 = __getpwnam(argv[2]);
printpwd(p1);
printpwd(p2);
return 0;
}
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