Taking user input in C++ without c++ standard library classes - c++

Question

I'm trying to take user input from the console without using the c++ standard library classes. Here's my code
while(true){
std::string line = " ";
while (getline(std::cin, line)) {
std::string arr[100];
int i = 0, len = 0;
for (int j=0; j < line.length(); j++) {
if(line[j] ==' ' || line[j] == '\n'){
std::string word = line.substr(i, j);
arr[len] = word;
len++;
i = j;
}
}
for (int k = 0; k <len ; ++k) {
std::cout<<arr[k]<<std::endl;
}
}
//break;
}
The idea is to identify each word and store it in an array. However this program only identifies the first word. Any idea, what am I doing wrong here.

Answer 1

In reading this, it would seem your problem lies on the line std::string word = line.substr(i, j);. You have to understand that substr's arguments are not "from i to j", but "from i, j characters". Read the documentation. :)
I haven't tested this, so it might not be perfect, but the principle is there.
while(true){
std::string line = " ";
while (getline(std::cin, line)) {
std::string arr[100];
int num_chars = 0, word = 0;
for (int i=0; i < line.length(); i++) {
/*We increment i, so every non-space character is one we
* will include in the word.*/
num_chars++;
if(line[i] ==' ' || line[i] == '\n'){
/*We want all characters from i to i+num_chars, that is
* we want all characters from j, forward i indices.
*/
std::string word = line.substr(i, num_chars);
arr[word] = word;
word++;
//We reset i here, in prep for parsing the next word.
i = 0;
}
}
for (int k = 0; k <len ; ++k) {
std::cout<<arr[k]<<std::endl;
}
}
//break;
}
Two other considerations:
1) Beware the single-letter variables, as it makes it far harder to read your code later. i is standard for a loop iterator or index, with j being the next when you're nesting for loops. However, i is not suitable for the "length of the word". Similarly, len is not suitable for the index of the word being stored. I changed the variables in the code to make it easier to read.
2) I would seriously consider revisiting your loop structure. while is common and very useful, but it is also highly prone to infinite loops. In fact, while(true) IS an infinite loop, so if you don't reach break for whatever reason, you'll wind up with some serious issues.
--
I would also agree that, if you want to avoid "STL" (and, actually std:: and stl are commonly confused, but are not the same thing...so let's say you want to avoid std), you'll want to avoid std::string and std::cin. Use C-strings and scanf/printf instead, as Nidhoegger suggested. It is more efficient than the std options, but it also more prone to the errors and "undefined behaviors" characteristic to C. It would take more effort, but would yield a more efficient result if you do it right.
While we're at it, I do NOT recommend std::stringstream unless your other tools cannot do the job well. That class has serious performance and efficiency problems, which are well-documented. I only recommend using it in cases where writing your own code with std::string and such would be either too laborious or have a high probability of being inefficient. This is NOT one of those cases.