【C语言程序设计第四版】例12-4代码

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

struct sysuser{
    char username[20];
    char password[8];
};
void encrypt_(char *pwd);
int checkUserValid(struct sysuser *psu);

int main(void){
    struct sysuser su;
    printf("Enter username: ");scanf("%s",su.username);
    printf("Enter password: ");scanf("%s",su.password);
    
    if (checkUserValid(&su)==1) {
        printf("Valid user!\n");
    }else{
        printf("Invalid user!\n");
    }
    
    return 0;
}

void encrypt_(char *pwd){
    int i;
    for (i = 0; i<strlen(pwd); i++) {
        pwd[i] = pwd[i]^15;
    }
}

int checkUserValid(struct sysuser *psu){
    FILE *fp;
    char usr[30], usr1[30], pwd[10];
    int check=0;
    
    strcpy(usr, psu->username);
    strcpy(pwd, psu->password);
    encrypt_(pwd);
    strcat(usr, " ");strcat(usr, pwd);strcat(usr, "\n");
    
    if ((fp = fopen("f12-2.txt", "r"))==NULL) {
        printf("File open error!\n");
        exit(0);
    }
    
    while (!feof(fp)) {
        fgets(usr1, 30, fp);    // 全文扫描，牛逼
        if (strcmp(usr, usr1) == 0) {
            check =1;break;
        }
    }
    
    if (fclose(fp)) {
        printf("Can not close the file!\n");
        exit(0);
    }
    
    return check;
}