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C++ alternative to sscanf()
I have the following line of code
sscanf(s, "%*s%d", &d);
How would I do this using istringstream?
I tried this:
istringstream stream(s);
(stream >> d);
But it is not correct because of *s in sscanf().
The %*s used with sscanf basically means to ignore a string (any characters up until a whitespace), and then after that you're telling it to read in an integer (%*s%d). The asterisk (*) has nothing to do with pointers in this case.
So using stringstreams, just emulate the same behaviour; read in a string that you can ignore before you read in the integer.
int d;
string dummy;
istringstream stream(s);
stream >> dummy >> d;
ie. With the following small program:
#include <iostream>
#include <sstream>
using namespace std;
int main(void)
{
string s = "abc 123";
int d;
string dummy;
istringstream stream(s);
stream >> dummy >> d;
cout << "The value of d is: " << d << ", and we ignored: " << dummy << endl;
return 0;
}
the output will be: The value of d is: 123, and we ignored: abc.
There is no pointer manipulation in your code.
As AusCBloke has said, you need to read the all of the unwanted characters before the int into a std::string. You also want to ensure that you handle malformed values of s, such as those with any integers.
#include <cassert>
#include <cstdio>
#include <sstream>
int main()
{
char s[] = "Answer: 42. Some other stuff.";
int d = 0;
sscanf(s, "%*s%d", &d);
assert(42 == d);
d = 0;
std::istringstream iss(s);
std::string dummy;
if (iss >> dummy >> d)
{
assert(dummy == "Answer:");
assert(42 == d);
}
else
{
assert(!"An error occurred and will be handled here");
}
}
Related
I am working on a project where I have to parse data from user input.
#include <iostream> // for cin and cout
#include <iomanip> // for setw()
#include <cctype> // for toupper()
using namespace std;
int main(){
string playerInput;
cin >> playerInput;
//Player would input strings like C13,C 6, I1, Z 16, etc...
}
return 0;
I've tried something like this, which kinda works but only if the letter proceeds the number in the string.
int myNr = std::stoi(playerInput);
What my end goal is to grab the letter and number from the string, and place them in a char variable and a integer variable respectively. I am stuck on how to proceed from here and could use some help, thanks!
This is the simplest and the shortest way to achieve that (it also ignores spaces and tabs):
int main() {
char ch;
int n;
cin >> ch >> n;
cout << "ch = " << ch << ", n = " << n << endl;
}
I think that other answers are a bit overcomplicated.
You could do like what you had:
char letter = playerInput.front();
playerInput.erase(0);
int number = std::stoi(playerInput);
Of course, that doesn't allow for spaces. Removing spaces can be quite tedious, but it could be done like:
playerInput.erase(
std::remove_if(
begin(playerInput), end(playerInput),
[](uint8_t ch) { return std::isspace(ch); }),
end(playerInput));
Full Demo
Live On Coliru
#include <cctype> // for toupper()
#include <iomanip> // for setw()
#include <iostream> // for cin and cout
#include <algorithm> // for remove_if
static bool ignorable(uint8_t ch) {
return std::isspace(ch)
|| std::ispunct(ch);
}
int main() {
std::string playerInput;
while (getline(std::cin, playerInput)) {
playerInput.erase(
std::remove_if(
begin(playerInput), end(playerInput),
ignorable),
end(playerInput));
if (playerInput.empty())
continue;
char letter = playerInput.front();
playerInput.erase(begin(playerInput));
int number = std::stoi(playerInput);
std::cout << "Got: " << letter << " with " << number << "\n";
}
}
Prints
Got: C with 13
Got: C with 6
Got: I with 1
Got: Z with 16
You have the right idea in using std::stoi. My code expands your approach:
string playerInput;
getline(cin, playerInput);
char c1 = playerInput[0];
int num = stoi(playerInput.substr(1));
The above code receives an input string, then takes out the first character and uses std::stoi on the rest of the string.
Note that I use std::getline to account for the possibility of there being spaces in the input. If you are doing this repeatedly, you will need to add cin.ignore() after each getline() statement. See this link for more info.
std::cin stops reading input when it encounters a space. You can use std::getline() if your input has spaces. To parse your string, you should check out std::stringstream. It allows you to read from a string as if it were a stream like std::cin.
#include <iostream> // for cin and cout
#include <iomanip> // for setw()
#include <cctype> // for toupper()
#include <sstream>
int main(){
std::string playerInput;
int i;
char c;
std::getline(std::cin, playerInput); // Remove trailing newline
std::getline(std::cin, playerInput);
//Player would input strings like C13,C 6, I1, Z 16, etc...
//String Stream
std::stringstream playerInputStream(playerInput);
//Read as if you were reading through cin
playerInputStream >> c; //
playerInputStream >> i;
}
return 0;
I'm using the following code:
string a, b, c;
cin >> a >> b >> c;
Explained: if a user inputs e.g. "hello new world hi"
then the mapping is a='hello', b='new' and c='world'. The "hi" will be ignored - and that's the problem!
What i want is, that in case of a wrong number of arguments (more or less than 3), the user should be forced to input again (maybe by an error message).
In your code, if you type in 4 words then the last word will exist somewhere on your machine(maybe on keyboard buffer). Thus, if you use cin to type value for another variable, the last word will be assign to the variable. So to check if user has typed error or not, you can do as following:
#include<iostream>
#include<string>
#include <sstream>
using namespace std;
int main()
{
string a, b, c;
cin >> a >> b >> c;
string check="";
getline(cin, check);
if (check != "")
{
cout << "input error,try again!";
}
return 0;
}
Use getline(cin, stringName)
After the input iterate through string check the index of spaces, and then split it into whatever you want.
You even don't need to declare three string to store. You can use std::getline.
std::string a;//,b,c;
std::getline(std::cin,a); //<< b << c;
std::cout <<a;
You can read whole line with std::getline, and then separate line by spaces. For example:
#include <string>
#include <vector>
#include <iostream>
// some code...
std::string text;
std::getline(std::cin, text);
std::vector<std::string> words;
int wordCount = 0;
while (auto space = text.find_first_of(' '))
{
wordCount++;
if (wordCount > 3)
{
std::cout << "Max 3 words!" << std::endl;
break;
}
words.push_back(text.substr(0, space));
text = text.substr(space + 1);
}
This way you will have max 3 words in vector words, you can get them by calling words[0] for first, etc. At 4th read word error is printed and while loop stops.
So guys, Actually What I wanna do here is that when I input 3,12,36 the output will be:
3
12
36
But here I have difficulty on how to make it output all the answer. What I have been doing is that when you input 3,12,36 it will output 3 12 only and if you type 3,12,36,48 it will output 3 12 36.
So it will always miss the last integer because my while loop is not correct I guess. but if I change it into
while(output >> life|| output >> ch)
It doesn't work either. I've done a lot of research but it still makes me confused and I'm still stuck on this part.
vector<int> parseInts(string str) {//23,4,56
vector<int>lifeishard;
stringstream output;
string lifeisgood = str;
output.str(lifeisgood);
int life;
char ch;
while(output >> life >> ch){
lifeishard.push_back(life);
//lifeishard.push_back(life2);
//lifeishard.push_back(life3);
}
return lifeishard;
}
int main() {
string str;
cin >> str;
vector<int> integers = parseInts(str);
for(int i = 0; i < integers.size(); i++) {
cout << integers[i] << "\n";
}
return 0;
}
On your last number, the while loop fails because there's no character at the end. Just the end of the string. So it doesn't execute the push_back inside the loop.
Change it so that the while loop just gets the number. Then do the push_back in the loop. Then in the loop, after the push, get the comma character. Don't bother checking for failure getting the comma because when it goes around the while loop again it will fail and exit.
I changed to using getline in your main. I changed your loop index to size_t because it is never a good idea to mix signed and unsigned integers, and whenever you use a size() function, it's a size_t. When posting your program it really should include everything. My fixed up version of your program:
#include <vector>
#include <string>
#include <iostream>
#include <sstream>
using namespace std;
vector<int> parseInts(string str) {//23,4,56
vector<int>lifeishard;
stringstream output;
string lifeisgood = str;
output.str(lifeisgood);
int life;
char ch;
while(output >> life){
lifeishard.push_back(life);
output >> ch;
}
return lifeishard;
}
int main() {
string str;
getline(cin, str);
vector<int> integers = parseInts(str);
for(size_t i = 0; i < integers.size(); i++) {
cout << integers[i] << "\n";
}
// Here is how we do for loops over containers in modern C++
for(auto x: integers) {
cout << x << '\n';
}
return 0;
}
A combination of stringstream, getline with delimiter and stoi would be enough for the conversion:
From the C++ reference for getline with delimiter:
Extracts characters from is and stores them into str until the delimitation character delim is found.
With this in mind, the code example below assumes the input is well-formed:
Example
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
vector<int> parseInts(const string& str, const char delim = ',')
{
vector<int> parsed;
stringstream ss(str);
string s;
while (getline(ss, s, delim)) // <- stores input in s upon hitting delimiter
parsed.push_back(stoi(s)); // <-- convert string to int and add it to parsed
return parsed;
}
int main()
{
string str = "3,12,36"; // <-- change to cin if you'd like
vector<int> ints = parseInts(str);
for (auto& i : ints)
cout << i << "\n";
}
Output
3
12
36
See more: getline, stoi
I have an input file that contains some data in coordinate mode
For example (2,3,5) translates to column 2, row 3, and level 5. I'm curious on a method of reading in the numbers after using getline(cin,string) to obtain the data. I don't know how many digits are in the data points so i can't assume the 1st character will be of length 1. Is there any libraries that can help solve the problem faster?
my gameplan so far that's not finished
void findNum(string *s){
int i;
int beginning =0;
bool foundBegin=0;
int end=0;
bool foundEnd=0
while(*s){
if(isNum(s)){//function that returns true if its a digit
if(!foundBegin){
foundBegin=1;
beginning=i;
}
}
if(foundBegin==1){
end=i;
foundBegin=0;
}
i++;
}
}
Try this:
#include <iostream>
#include <cstdlib>
#include <sstream>
#include <vector>
#include <string>
int main() {
std::vector <std::string> params;
std::string str;
std::cout << "Enter the parameter string: " << std::endl;
std::getline(cin, str);//use getline instead of cin here because you want to capture all the input which may or may not be whitespace delimited.
std::istringstream iss(str);
std::string temp;
while (std::getline(iss, temp, ',')) {
params.push_back(temp);
}
for (std::vector<std::string>::const_iterator it=params.begin(); it != params.end(); ++it) {
std::cout << *it << std::endl;
}
return 0;
}
The only caveat is that the arguments will have to be non whitespace delimited.
Example input string:
1,2,3
Output:
1
2
3
Once these arguments have been parsed, you can then convert them from strings to (example) integer via the following:
template <typename T>
T convertToType(const std::string &stringType) {
std::stringstream iss(stringType);
T rtn;
return iss >> rtn ? rtn : 0;
}
which can be used as follows:
int result = convertToType<int>("1");//which will assign result to a value of 1.
UPDATE:
This now works correctly on whitespace delimited input (except for newlines) like the following:
1 , 2, 3 , 4
Which yields:
1
2
3
4
jrd1's answer is pretty good, but if you'd prefer there happen to be functions for converting characters to integers (and back) already in the C standard library (cstdlib). You'd be looking for atoi.
http://en.cppreference.com/w/cpp/string/byte/atoi
#include <sstream>
void findNums(const string &str, int &i, int &j, int &k)
{
std::stringstream ss(str);
char c;
ss >> c >> i >> c >> j >> c >> k;
}
Simply use extractor operator for reading any type of value in respective variable type.
#incude<ifstream> // for reading from file
#include<iostream>
using namespace std;
int main()
{
int number;
ifstream fin ("YouFileName", std::ifstream::in);
fin >> number; // put next INT no matter how much digit it have in number
while(!fin.eof())
{
cout << number << endl;
fin >> number; // put next INT no matter how much digit it have in number and it will ignore all non-numeric characters between two numbers as well.
}
fin.close();
return 0;
}
Have a look over here for more details.
Note: Be careful while using it for character arrays and strings.. :)
#include <iostream>
#include <sstream>
using namespace std;
int get_4()
{
char c = '4';
stringstream s(ios::in);
s << c;
int i;
s >> i;
return i;
}
int main()
{
cout << get_4() << endl;
}
The conversion is not working for me. If I write a character '4' or character array {'4','\0'} to stringstream and then read it out to int i, I don't get back the 4. What is wrong with the above code?
Because you set the stringstream to input-only -- no output.
If you check the fail() bit after trying to extract the int, you'll see it didn't work:
s >> i;
bool b = s.fail();
if( b )
cerr << "WHOA DOGGIE! WE BLOWED UP\n";
In your code, change:
stringstream s(ios::in);
to:
stringstream s;