converting from strings to ints - c++

I would like to know what is the easiest way to convert an int to C++ style string and from C++ style string to int.
edit
Thank you very much. When converting form string to int what happens if I pass a char string ? (ex: "abce").
Thanks & Regards,
Mousey

Probably the easiest is to use operator<< and operator>> with a stringstream (you can initialize a stringstream from a string, and use the stream's .str() member to retrieve a string after writing to it.
Boost has a lexical_cast that makes this particularly easy (though hardly a paragon of efficiency). Normal use would be something like int x = lexical_cast<int>(your_string);

You can change "%x" specifier to "%d" or any other format supported by sprintf. Ensure to appropriately adjust the buffer size 'buf'
int main(){
char buf[sizeof(int)*2 + 1];
int x = 0x12345678;
sprintf(buf, "%x", x);
string str(buf);
int y = atoi(str.c_str());
}
EDIT 2:
int main(){
char buf[sizeof(int)*2 + 1];
int x = 42;
sprintf(buf, "%x", x);
string str(buf);
//int y = atoi(str.c_str());
int y = static_cast<int>(strtol(str.c_str(), NULL, 16));
}

This is to convert string to number.
#include "stdafx.h"
#include <iostream>
#include <string>
#include <sstream>
int convert_string_to_number(const std::string& st)
{
std::istringstream stringinfo(st);
int num = 0;
stringinfo >> num;
return num;
}
int main()
{
int number = 0;
std::string number_as_string("425");
number = convert_string_to_number(number_as_string);
std::cout << "The number is " << number << std::endl;
std::cout << "Number of digits are " << number_as_string.length() << std::endl;
}
Like wise, the following is to convert number to string.
#include "stdafx.h"
#include <iostream>
#include <string>
#include <sstream>
std::string convert_number_to_string(const int& number_to_convert)
{
std::ostringstream os;
os << number_to_convert;
return (os.str());
}
int main()
{
int number = 425;
std::string stringafterconversion;
stringafterconversion = convert_number_to_string(number);
std::cout << "After conversion " << stringafterconversion << std::endl;
std::cout << "Number of digits are " << stringafterconversion.length() << std::endl;
}

Use atoi to convert a string to an int. Use a stringstream to convert the other way.

Related

c++ converting int to char + add leading zeros to char

I got numbers from 0 to 999. How can I achieve the following
int i = 123;//possible values 0-999
char i_char[3] = /*do conversion of int i to char and add 3 leading zeros*/
Example(s): i_char shall look like "001" for i=1, "011" for i=11 or "101" for i=101
Use a std::ostringstream with std::setfill() and std::setw(), eg:
#include <string>
#include <sstream>
#include <iomanip>
int i = ...;
std::ostringstream oss;
oss << std::setfill('0') << std::setw(3) << i;
std::string s = oss.str();
It appears you are looking for sprintf, or perhaps printf.
int i = 123;
char str[10];
sprintf(str, "%03d", i);
Since, you tagged the question with c++ here is a quick solution using std::string and std::to_string:
#include <iostream>
#include <string>
int main() {
int i = 1;
std::string s = std::to_string(i);
if ( s.size() < 3 )
s = std::string(3 - s.size(), '0') + s;
std::cout << s << std::endl;
return 0;
}
For i=1 it will output: 001.

Converting char to int c++

I'm loosing my mind at the moment and below is what I'm trying to do.
char* buffer;
sprintf(buffer, "0x%08x", 5);
*(int *)(0x834AF2AC + 0x1a) = ?buffer?;
Buffer = 0x05000000
I need to set that in memory, if I just set 05 it will set 0x00000005
Question asked better.
How can I convert an INT into a format of "0x%08x"
So 5 becomes 0x05000000
ANSWERD:
The correct answer is *(int *)(0x834AF2AC + 0x1a) = 5<<24;
Something like this:
#include <iostream> // for std::cout, std::endl
#include <string> // for std::string, std::stoi
int main()
{
std::string s{"0x05"};
int i = std::stoi(s, nullptr, 16); // convert base 16 number in s to int
std::cout << i << std::endl;
}
Two result from google which points to stackoverflow (result 1 and 2).
Convert char to int in C and C++
C char* to int conversion
I'm not sure if I understand correctly but if you want to convert an entire string to int, then I would suggest stringstream.
http://www.cplusplus.com/reference/sstream/stringstream/stringstream/
For hexadecimal string:
#include <string> // std::string
#include <iostream> // std::cout
#include <sstream> // std::stringstream
int main () {
std::stringstream ss;
ss << std::hex << 0x05;
int foo;
ss >> foo;
std::cout << "foo: " << foo << '\n';
return 0;
}

c++ double to string shows floating points

I have a string: (66)
Then I convert it to double and do some math: atof(t.c_str()) / 30
then I convert it back to string: string s = boost::lexical_cast<string>(hizdegerd)
Problem is when I show it on label it becomes 2,20000001.
I've tried everything. sprintf etc.
I want to show only one digit after point.
hizdegerd = atof(t.c_str()) / 30;
char buffer [50];
hizdegerd=sprintf (buffer, "%2.2f",hizdegerd);
if(oncekideger != hizdegerd)
{
txtOyunHiz->SetValue(hizdegerd);
oncekideger = hizdegerd;
}
I think I'd wrap the formatting up into a function template, something like this:
#include <iostream>
#include <sstream>
#include <iomanip>
template <class T>
std::string fmt(T in, int width = 0, int prec = 0) {
std::ostringstream s;
s << std::setw(width) << std::setprecision(prec) << in;
return s.str();
}
int main(){
std::string s = fmt(66.0 / 30.0, 2, 2);
std::cout << s << "\n";
}
You can use this way of conversion back to string and then only the wished number of digits for the precision will be taken in consideration:
ostringstream a;
a.precision(x); // the number of precision digits will be x-1
double b = 1.45612356;
a << b;
std::string s = a.str();
Since you wrote "I want to show":
#include<iostream>
#include<iomanip>
int main()
{
std::cout << std::fixed << std::setprecision(1) << 34.2356457;
}
Output:
34.2
By the way, sprintf is buffer-overflow-vulnerable and is not C++ .

convert string to integer in c++

Hello
I know it was asked many times but I hadn't found answer to my specific question.
I want to convert only string that contains only decimal numbers:
For example 256 is OK but 256a is not.
Could it be done without checking the string?
Thanks
The simplest way that makes error checking optional that I can think of is this:
char *endptr;
int x = strtol(str, &endptr, 0);
int error = (*endptr != '\0');
In C++ way, use stringstream:
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
stringstream sstr;
int a = -1;
sstr << 256 << 'a';
sstr >> a;
if (sstr.failbit)
{
cout << "Either no character was extracted, or the character can't represent a proper value." << endl;
}
if (sstr.badbit)
{
cout << "Error on stream.\n";
}
cout << "Extracted number " << a << endl;
return 0;
}
An other way using c++ style : We check the number of digits to know if the string was valid or not :
#include <iostream>
#include <sstream>
#include <string>
#include <cmath>
int main(int argc,char* argv[]) {
std::string a("256");
std::istringstream buffer(a);
int number;
buffer >> number; // OK conversion is done !
// Let's now check if the string was valid !
// Quick way to compute number of digits
size_t num_of_digits = (size_t)floor( log10( abs( number ) ) ) + 1;
if (num_of_digits!=a.length()) {
std::cout << "Not a valid string !" << std::endl;
}
else {
std::cout << "Valid conversion to " << number << std::endl;
}
}

How to concatenate a std::string and an int

I thought this would be really simple, but it's presenting some difficulties. If I have
std::string name = "John";
int age = 21;
How do I combine them to get a single string "John21"?
In alphabetical order:
std::string name = "John";
int age = 21;
std::string result;
// 1. with Boost
result = name + boost::lexical_cast<std::string>(age);
// 2. with C++11
result = name + std::to_string(age);
// 3. with FastFormat.Format
fastformat::fmt(result, "{0}{1}", name, age);
// 4. with FastFormat.Write
fastformat::write(result, name, age);
// 5. with the {fmt} library
result = fmt::format("{}{}", name, age);
// 6. with IOStreams
std::stringstream sstm;
sstm << name << age;
result = sstm.str();
// 7. with itoa
char numstr[21]; // enough to hold all numbers up to 64-bits
result = name + itoa(age, numstr, 10);
// 8. with sprintf
char numstr[21]; // enough to hold all numbers up to 64-bits
sprintf(numstr, "%d", age);
result = name + numstr;
// 9. with STLSoft's integer_to_string
char numstr[21]; // enough to hold all numbers up to 64-bits
result = name + stlsoft::integer_to_string(numstr, 21, age);
// 10. with STLSoft's winstl::int_to_string()
result = name + winstl::int_to_string(age);
// 11. With Poco NumberFormatter
result = name + Poco::NumberFormatter().format(age);
is safe, but slow; requires Boost (header-only); most/all platforms
is safe, requires C++11 (to_string() is already included in #include <string>)
is safe, and fast; requires FastFormat, which must be compiled; most/all platforms
(ditto)
is safe, and fast; requires the {fmt} library, which can either be compiled or used in a header-only mode; most/all platforms
safe, slow, and verbose; requires #include <sstream> (from standard C++)
is brittle (you must supply a large enough buffer), fast, and verbose; itoa() is a non-standard extension, and not guaranteed to be available for all platforms
is brittle (you must supply a large enough buffer), fast, and verbose; requires nothing (is standard C++); all platforms
is brittle (you must supply a large enough buffer), probably the fastest-possible conversion, verbose; requires STLSoft (header-only); most/all platforms
safe-ish (you don't use more than one int_to_string() call in a single statement), fast; requires STLSoft (header-only); Windows-only
is safe, but slow; requires Poco C++ ; most/all platforms
In C++11, you can use std::to_string, e.g.:
auto result = name + std::to_string( age );
If you have Boost, you can convert the integer to a string using boost::lexical_cast<std::string>(age).
Another way is to use stringstreams:
std::stringstream ss;
ss << age;
std::cout << name << ss.str() << std::endl;
A third approach would be to use sprintf or snprintf from the C library.
char buffer[128];
snprintf(buffer, sizeof(buffer), "%s%d", name.c_str(), age);
std::cout << buffer << std::endl;
Other posters suggested using itoa. This is NOT a standard function, so your code will not be portable if you use it. There are compilers that don't support it.
#include <iostream>
#include <sstream>
std::ostringstream o;
o << name << age;
std::cout << o.str();
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
string itos(int i) // convert int to string
{
stringstream s;
s << i;
return s.str();
}
Shamelessly stolen from http://www.research.att.com/~bs/bs_faq2.html.
This is the easiest way:
string s = name + std::to_string(age);
If you have C++11, you can use std::to_string.
Example:
std::string name = "John";
int age = 21;
name += std::to_string(age);
std::cout << name;
Output:
John21
It seems to me that the simplest answer is to use the sprintf function:
sprintf(outString,"%s%d",name,age);
#include <string>
#include <sstream>
using namespace std;
string concatenate(std::string const& name, int i)
{
stringstream s;
s << name << i;
return s.str();
}
#include <sstream>
template <class T>
inline std::string to_string (const T& t)
{
std::stringstream ss;
ss << t;
return ss.str();
}
Then your usage would look something like this
std::string szName = "John";
int numAge = 23;
szName += to_string<int>(numAge);
cout << szName << endl;
Googled [and tested :p ]
This problem can be done in many ways. I will show it in two ways:
Convert the number to string using to_string(i).
Using string streams.
Code:
#include <string>
#include <sstream>
#include <bits/stdc++.h>
#include <iostream>
using namespace std;
int main() {
string name = "John";
int age = 21;
string answer1 = "";
// Method 1). string s1 = to_string(age).
string s1=to_string(age); // Know the integer get converted into string
// where as we know that concatenation can easily be done using '+' in C++
answer1 = name + s1;
cout << answer1 << endl;
// Method 2). Using string streams
ostringstream s2;
s2 << age;
string s3 = s2.str(); // The str() function will convert a number into a string
string answer2 = ""; // For concatenation of strings.
answer2 = name + s3;
cout << answer2 << endl;
return 0;
}
In C++20 you'll be able to do:
auto result = std::format("{}{}", name, age);
In the meantime you can use the {fmt} library, std::format is based on:
auto result = fmt::format("{}{}", name, age);
Disclaimer: I'm the author of the {fmt} library and C++20 std::format.
If you'd like to use + for concatenation of anything which has an output operator, you can provide a template version of operator+:
template <typename L, typename R> std::string operator+(L left, R right) {
std::ostringstream os;
os << left << right;
return os.str();
}
Then you can write your concatenations in a straightforward way:
std::string foo("the answer is ");
int i = 42;
std::string bar(foo + i);
std::cout << bar << std::endl;
Output:
the answer is 42
This isn't the most efficient way, but you don't need the most efficient way unless you're doing a lot of concatenation inside a loop.
If you are using MFC, you can use a CString
CString nameAge = "";
nameAge.Format("%s%d", "John", 21);
Managed C++ also has a
string formatter.
As a one liner: name += std::to_string(age);
The std::ostringstream is a good method, but sometimes this additional trick might get handy transforming the formatting to a one-liner:
#include <sstream>
#define MAKE_STRING(tokens) /****************/ \
static_cast<std::ostringstream&>( \
std::ostringstream().flush() << tokens \
).str() \
/**/
Now you can format strings like this:
int main() {
int i = 123;
std::string message = MAKE_STRING("i = " << i);
std::cout << message << std::endl; // prints: "i = 123"
}
As a Qt-related question was closed in favour of this one, here's how to do it using Qt:
QString string = QString("Some string %1 with an int somewhere").arg(someIntVariable);
string.append(someOtherIntVariable);
The string variable now has someIntVariable's value in place of %1 and someOtherIntVariable's value at the end.
There are more options possible to use to concatenate integer (or other numerric object) with string. It is Boost.Format
#include <boost/format.hpp>
#include <string>
int main()
{
using boost::format;
int age = 22;
std::string str_age = str(format("age is %1%") % age);
}
and Karma from Boost.Spirit (v2)
#include <boost/spirit/include/karma.hpp>
#include <iterator>
#include <string>
int main()
{
using namespace boost::spirit;
int age = 22;
std::string str_age("age is ");
std::back_insert_iterator<std::string> sink(str_age);
karma::generate(sink, int_, age);
return 0;
}
Boost.Spirit Karma claims to be one of the fastest option for integer to string conversion.
std::ostringstream
#include <sstream>
std::ostringstream s;
s << "John " << age;
std::string query(s.str());
std::to_string (C++11)
std::string query("John " + std::to_string(age));
boost::lexical_cast
#include <boost/lexical_cast.hpp>
std::string query("John " + boost::lexical_cast<std::string>(age));
Here is an implementation of how to append an int to a string using the parsing and formatting facets from the IOStreams library.
#include <iostream>
#include <locale>
#include <string>
template <class Facet>
struct erasable_facet : Facet
{
erasable_facet() : Facet(1) { }
~erasable_facet() { }
};
void append_int(std::string& s, int n)
{
erasable_facet<std::num_put<char,
std::back_insert_iterator<std::string>>> facet;
std::ios str(nullptr);
facet.put(std::back_inserter(s), str,
str.fill(), static_cast<unsigned long>(n));
}
int main()
{
std::string str = "ID: ";
int id = 123;
append_int(str, id);
std::cout << str; // ID: 123
}
Common Answer: itoa()
This is bad. itoa is non-standard, as pointed out here.
You can concatenate int to string by using the given below simple trick, but note that this only works when integer is of single digit. Otherwise, add integer digit by digit to that string.
string name = "John";
int age = 5;
char temp = 5 + '0';
name = name + temp;
cout << name << endl;
Output: John5
There is a function I wrote, which takes the int number as the parameter, and convert it to a string literal. This function is dependent on another function that converts a single digit to its char equivalent:
char intToChar(int num)
{
if (num < 10 && num >= 0)
{
return num + 48;
//48 is the number that we add to an integer number to have its character equivalent (see the unsigned ASCII table)
}
else
{
return '*';
}
}
string intToString(int num)
{
int digits = 0, process, single;
string numString;
process = num;
// The following process the number of digits in num
while (process != 0)
{
single = process % 10; // 'single' now holds the rightmost portion of the int
process = (process - single)/10;
// Take out the rightmost number of the int (it's a zero in this portion of the int), then divide it by 10
// The above combination eliminates the rightmost portion of the int
digits ++;
}
process = num;
// Fill the numString with '*' times digits
for (int i = 0; i < digits; i++)
{
numString += '*';
}
for (int i = digits-1; i >= 0; i--)
{
single = process % 10;
numString[i] = intToChar ( single);
process = (process - single) / 10;
}
return numString;
}
In C++ 20 you can have a variadic lambda that does concatenate arbitrary streamable types to a string in a few lines:
auto make_string=[os=std::ostringstream{}](auto&& ...p) mutable
{
(os << ... << std::forward<decltype(p)>(p) );
return std::move(os).str();
};
int main() {
std::cout << make_string("Hello world: ",4,2, " is ", 42.0);
}
see https://godbolt.org/z/dEe9h75eb
using move(os).str() guarantees that the ostringstream object's stringbuffer is empty next time the lambda is called.
You can use the C function itoa() like this:
char buf[3];
itoa(age, buf, 10);
name += buf;