为什么puts函数不能与C ++中套接字的输入字符一起使用？

Question

This is my code for a server running a login manager, that log into a file the malicious access and print out the result of the wrong login. The chars user and pass come from the user input using the socket.

if ((memcmp(user, "admin", strlen("admin")) == 0)) {
    /*code... */
}
else {
    char msg[600];
    strcpy (msg,"Login error with ");
    strcat (msg,"user: ");
    strcat (msg,user);
    strcat (msg," password: ");
    strcat (msg,pass);
    strcat (msg," from: ");
    strcat (msg, client_ip);
    puts (msg);
    logfile->Write(msg);
    return false;
}

Well, the problem is the output both on the output console and in the logfile.

Like this:

Login error with user: lol

 password: asd

:��ܔ��P{w� from: 127.0.0.1

Why are there the strange asci chars? How can avoid the new line since they come from user input by socket?

Answer 1

As multiple people have commented about, this snippet of code contains nothing C++ specific, so I'm answering as if you are working in plain C.

I'm guessing, since you use memcmp above, that your input strings are not null terminated. strcat will keep on appending char s from whatever the pointer wanders into until it runs into a '\\0' . You'll need to add a null terminator if you want to use user or password as a C-style string, or else use strncat and pass the length.

Also, beware of overrunning msg . You might have better luck using snprintf to format your message, since it accepts a maximum output string length.

Answer 2

This way you could make your code little bit smaller

if (strcmp(user, "admin") == 0) {
    /* yahoo, admin! */
}
else {
    char buff[256];
    snprintf(buff, sizeof(buff),
            "Login error with user: %s password: %s from: %s",
            user,
            pass,
            client_ip);
    printf("%s\n", buff);
    logfile->Write(buff);
    return false;
}

adding this extra code before if-statement you could ensure strings are valid

printf("user, len:%d, value: %s\n", strlen(user), user);
printf("pass, len:%d, value: %s\n", strlen(pass), pass);
printf("client_ip, len:%d, value: %s\n", strlen(client_ip), client_ip);