C++ how to detect whitespace - c++

Question

I am creating a program that allows users to key in their user name and password. the problem is, when the system prompts to "Enter userName:" and I hit enter key, it will print out "Name cannot contain a blank"
but if I hit a FEW spaceBars and hit enter key and make it blank field after that ,it skips to prompt the user to enter the password without printing out "Name cannot contain a blank" and prompting the user to enter the userName again.
how should I change my codes to ensure that it will still prompt the user to enter the userName again even though I hit a spacebars and hit enter? please advise. thanks
code
string userName=" ";
string password;
cout << "Enter UserName:";
while (getline(cin, userName)) {
if (userName.empty()) {
cout << "Name cannot contain a blank."<< endl;
cout << "Enter userName:";
userName = userName;
//throw errorMsg;
}
if(!userName.empty()) {
cout << "Enter Password";
}
}

Answer 1

Username validation is not trivial, for many reasons. You don't want to be in the business of manufacturing what you "think" the user wanted to type, while at the same time it is clear you want to avoid a potentially long validation of what is going to be invalid.
In the end, I would suspect you can simply take the prospect entry, strip all the whitespace, and if there is anything left over, submit the original entry for validation. Don't bite off the business of validating something the user may have meant to type. I.e.
"\t\t "
should be grounds for a re-prompt, while
"John Smith"
"\t WillJohnson "
"Gary"
should all be submitted verbatim, and let the chips fall where they may.
That said,
bool isValidUserName(std::string name)
{
name.erase(std::remove_if(name.begin(), name.end(),
[](char c){ return std::isspace(static_cast<unsigned char>(c));}), name.end());
return !name.empty();
}
should do that for you. A sample is below:
int main()
{
std::cout << std::boolalpha << isValidUserName("\t \t ") << std::endl;
std::cout << std::boolalpha << isValidUserName("\t Will Johnson ") << std::endl;
return 0;
}
Output
false
true

Answer 2

Assuming a C++11 compliant compiler your test for spaces could be using std::find_if
if (std::find_if(userName.begin(), userName.end(), isspace))
!= userName.end())
or
if (std::find_if(userName.begin(), userName.end(),
[=](char c){return isspace(c);}) != userName.end())
Notice that several characters are space-like ' ' but also '\t' (tabulation) etc...

Answer 3

just consider the space as a character and increment it when you find it

Answer 4

The logic is to check if the starting character of the username is a blank space and also the last slot of the string is not a blank space.
example :
This should be accepted = "a b".
But
this should not be " a ".
or this should not be " a".
or this should not be "a ".
if (userName[0]!=" " && userName[userName.size()]!=" "){
//accept this case and move on.
}
else{
//reject all other cases.
}

Answer 5

#include <iostream>
#include <vector>
using namespace std;
int main(){
string username, password;
int un = 1;
int ps = 1;
while(un){
cout<<"Username:";
getline(cin,username);
int usize = username.size();
vector <string> v ;
v.insert(v.begin(), username);
if (usize==1){
if(username==" "){
cout<<"Username can not be blank"<<endl;
}
else{
un=0;
}
}
else{
int check=0; int trim = 0;
for (int i=0; i<usize; i++){
if (username[i]!=' '){
check=1;
trim = i;
break;
}
}
if(check==1){
un=0;
}
else{
}
}
}
while(ps){
cout<<"Password:";
getline(cin,password);
int usize = password.size();
vector <string> v ;
v.insert(v.begin(), password);
if (usize==1){
if(password==" "){
cout<<"Password can not be blank"<<endl;
}
else{
ps=0;
}
}
else{
int check=0;
for (int i=0; i<usize; i++){
if (password[i]!=' '){
check=1;
break;
}
}
if(check==1){
ps=0;
}
else{
}
}
}
cout<<endl;
cout<<"----------------------------------------------"<<endl;
cout<<"Username is: "<<username<<endl;
cout<<"Password is: "<<password<<endl;
return 0;
}

Answer 6

Check if the string is empty if so then do the empty validation
If the string is not empty then check if it has spaces i.e find_first_not_of("\t ") if this returns number greater than 0 we know the username has leading white/tab spaces followed by zero or more characters. i.e leading spaces then the username
Its upto you to now do the validation for a good username.
#include <iostream>
#include <cstring>
using namespace std;
int main() {
string userName = " ";
string password;
cout << "Enter UserName:";
while(getline(cin, userName)) {
if(userName.empty()) {
cout << "Empty String";
} else if(userName.find_first_not_of("\t ") > 0) {
cout << "Could contain spaces followed by username or just spaces";
} else {
cout << "User Name is Valid";
}
}
return 0;
}