I have a string in byte that represent a double number. It is like this in hexadecimal format:
char buffer[17] = "4053E60C49BA5E35";
In double the correct value is: 21,898625.
I need a simple way to convert this string in double. The only way that work just now is this, but I'm not sure it this the best way:
double hexstr2double(const std::string& hexstr)
{
union
{
long long i;
double d;
} value;
try{
value.i = std::stoll(hexstr, nullptr, 16);
}
catch(...){value.i=0;}
return value.d;
}
Thank you
You can use reinterpret_cast instead of the union.
Also the value you presented is different on a site for conversion from hex to double: https://gregstoll.com/~gregstoll/floattohex/
#include <iostream>
using namespace std;
double hexstr2double(const std::string& hexstr)
{
double d = 0.0;
try{
*reinterpret_cast<unsigned long long*>(&d) = std::stoull(hexstr, nullptr, 16);
}
catch(...){}
return d;
}
int main()
{
char buffer[] = "4035e60c49ba5e35";
cout<<sizeof(double)<<" "<<sizeof(unsigned long long)<<endl;
cout<<hexstr2double(buffer);
return 0;
}
Related
I want to convert a hex string to a 32 bit signed integer in C++.
So, for example, I have the hex string "fffefffe". The binary representation of this is 11111111111111101111111111111110. The signed integer representation of this is: -65538.
How do I do this conversion in C++? This also needs to work for non-negative numbers. For example, the hex string "0000000A", which is 00000000000000000000000000001010 in binary, and 10 in decimal.
use std::stringstream
unsigned int x;
std::stringstream ss;
ss << std::hex << "fffefffe";
ss >> x;
the following example produces -65538 as its result:
#include <sstream>
#include <iostream>
int main() {
unsigned int x;
std::stringstream ss;
ss << std::hex << "fffefffe";
ss >> x;
// output it as a signed type
std::cout << static_cast<int>(x) << std::endl;
}
In the new C++11 standard, there are a few new utility functions which you can make use of! specifically, there is a family of "string to number" functions (http://en.cppreference.com/w/cpp/string/basic_string/stol and http://en.cppreference.com/w/cpp/string/basic_string/stoul). These are essentially thin wrappers around C's string to number conversion functions, but know how to deal with a std::string
So, the simplest answer for newer code would probably look like this:
std::string s = "0xfffefffe";
unsigned int x = std::stoul(s, nullptr, 16);
NOTE: Below is my original answer, which as the edit says is not a complete answer. For a functional solution, stick the code above the line :-).
It appears that since lexical_cast<> is defined to have stream conversion semantics. Sadly, streams don't understand the "0x" notation. So both the boost::lexical_cast and my hand rolled one don't deal well with hex strings. The above solution which manually sets the input stream to hex will handle it just fine.
Boost has some stuff to do this as well, which has some nice error checking capabilities as well. You can use it like this:
try {
unsigned int x = lexical_cast<int>("0x0badc0de");
} catch(bad_lexical_cast &) {
// whatever you want to do...
}
If you don't feel like using boost, here's a light version of lexical cast which does no error checking:
template<typename T2, typename T1>
inline T2 lexical_cast(const T1 &in) {
T2 out;
std::stringstream ss;
ss << in;
ss >> out;
return out;
}
which you can use like this:
// though this needs the 0x prefix so it knows it is hex
unsigned int x = lexical_cast<unsigned int>("0xdeadbeef");
For a method that works with both C and C++, you might want to consider using the standard library function strtol().
#include <cstdlib>
#include <iostream>
using namespace std;
int main() {
string s = "abcd";
char * p;
long n = strtol( s.c_str(), & p, 16 );
if ( * p != 0 ) { //my bad edit was here
cout << "not a number" << endl;
}
else {
cout << n << endl;
}
}
Andy Buchanan, as far as sticking to C++ goes, I liked yours, but I have a few mods:
template <typename ElemT>
struct HexTo {
ElemT value;
operator ElemT() const {return value;}
friend std::istream& operator>>(std::istream& in, HexTo& out) {
in >> std::hex >> out.value;
return in;
}
};
Used like
uint32_t value = boost::lexical_cast<HexTo<uint32_t> >("0x2a");
That way you don't need one impl per int type.
Working example with strtoul will be:
#include <cstdlib>
#include <iostream>
using namespace std;
int main() {
string s = "fffefffe";
char * p;
long n = strtoul( s.c_str(), & p, 16 );
if ( * p != 0 ) {
cout << "not a number" << endl;
} else {
cout << n << endl;
}
}
strtol converts string to long. On my computer numeric_limits<long>::max() gives 0x7fffffff. Obviously that 0xfffefffe is greater than 0x7fffffff. So strtol returns MAX_LONG instead of wanted value. strtoul converts string to unsigned long that's why no overflow in this case.
Ok, strtol is considering input string not as 32-bit signed integer before convertation. Funny sample with strtol:
#include <cstdlib>
#include <iostream>
using namespace std;
int main() {
string s = "-0x10002";
char * p;
long n = strtol( s.c_str(), & p, 16 );
if ( * p != 0 ) {
cout << "not a number" << endl;
} else {
cout << n << endl;
}
}
The code above prints -65538 in console.
Here's a simple and working method I found elsewhere:
string hexString = "7FF";
int hexNumber;
sscanf(hexString.c_str(), "%x", &hexNumber);
Please note that you might prefer using unsigned long integer/long integer, to receive the value.
Another note, the c_str() function just converts the std::string to const char* .
So if you have a const char* ready, just go ahead with using that variable name directly, as shown below [I am also showing the usage of the unsigned long variable for a larger hex number. Do not confuse it with the case of having const char* instead of string]:
const char *hexString = "7FFEA5"; //Just to show the conversion of a bigger hex number
unsigned long hexNumber; //In case your hex number is going to be sufficiently big.
sscanf(hexString, "%x", &hexNumber);
This works just perfectly fine (provided you use appropriate data types per your need).
I had the same problem today, here's how I solved it so I could keep lexical_cast<>
typedef unsigned int uint32;
typedef signed int int32;
class uint32_from_hex // For use with boost::lexical_cast
{
uint32 value;
public:
operator uint32() const { return value; }
friend std::istream& operator>>( std::istream& in, uint32_from_hex& outValue )
{
in >> std::hex >> outValue.value;
}
};
class int32_from_hex // For use with boost::lexical_cast
{
uint32 value;
public:
operator int32() const { return static_cast<int32>( value ); }
friend std::istream& operator>>( std::istream& in, int32_from_hex& outValue )
{
in >> std::hex >> outvalue.value;
}
};
uint32 material0 = lexical_cast<uint32_from_hex>( "0x4ad" );
uint32 material1 = lexical_cast<uint32_from_hex>( "4ad" );
uint32 material2 = lexical_cast<uint32>( "1197" );
int32 materialX = lexical_cast<int32_from_hex>( "0xfffefffe" );
int32 materialY = lexical_cast<int32_from_hex>( "fffefffe" );
// etc...
(Found this page when I was looking for a less sucky way :-)
Cheers,
A.
just use stoi/stol/stoll
for example:
std::cout << std::stol("fffefffe", nullptr, 16) << std::endl;
output: 4294901758
This worked for me:
string string_test = "80123456";
unsigned long x;
signed long val;
std::stringstream ss;
ss << std::hex << string_test;
ss >> x;
// ss >> val; // if I try this val = 0
val = (signed long)x; // However, if I cast the unsigned result I get val = 0x80123456
Try this. This solution is a bit risky. There are no checks. The string must only have hex values and the string length must match the return type size. But no need for extra headers.
char hextob(char ch)
{
if (ch >= '0' && ch <= '9') return ch - '0';
if (ch >= 'A' && ch <= 'F') return ch - 'A' + 10;
if (ch >= 'a' && ch <= 'f') return ch - 'a' + 10;
return 0;
}
template<typename T>
T hextot(char* hex)
{
T value = 0;
for (size_t i = 0; i < sizeof(T)*2; ++i)
value |= hextob(hex[i]) << (8*sizeof(T)-4*(i+1));
return value;
};
Usage:
int main()
{
char str[4] = {'f','f','f','f'};
std::cout << hextot<int16_t>(str) << "\n";
}
Note: the length of the string must be divisible by 2
For those looking to convert number base for unsigned numbers, it is pretty trivial to do yourself in both C/C++ with minimal dependency (only operator not provided by the language itself is pow() function).
In mathematical terms, a positive ordinal number d in base b with n number of digits can be converted to base 10 using:
Example: Converting base 16 number 00f looks like:
= 0*16^2 + 0*16^1 + 16*16^0 = 15
C/C++ Example:
#include <math.h>
unsigned int to_base10(char *d_str, int len, int base)
{
if (len < 1) {
return 0;
}
char d = d_str[0];
// chars 0-9 = 48-57, chars a-f = 97-102
int val = (d > 57) ? d - ('a' - 10) : d - '0';
int result = val * pow(base, (len - 1));
d_str++; // increment pointer
return result + to_base10(d_str, len - 1, base);
}
int main(int argc, char const *argv[])
{
char n[] = "00f"; // base 16 number of len = 3
printf("%d\n", to_base10(n, 3, 16));
}
I am copying double value into unsigned char* in the following way.
unsigned char* cmdBody;
double val = (double)-1;
std::ostringstream sstream;
sstream << val;
std::string valString = sstream.str();
unsigned int dataSize = valString.size() + 1;
cmdBody = (unsigned char*)malloc(dataSize);
memset(cmdBody, 0, dataSize);
memcpy(cmdBody, (unsigned char*)valString.c_str(), dataSize - 1);
cmdBody[dataSize - 1] = '\0';
From cmdBody I need to convert the value into double type. How to do it?
C much?
Your solution is very simple if you just use a std::string:
const auto val = -1.0; // Input double
const auto cmdBody = std::to_string(val); // Convert double to a std::string
const auto foo = std::stod(cmdBody); // Convert std::string to a double
It's important to note that there is no need to allocate, memcopy, or null-terminate when constructing a std::string. Which vastly simplifies your code.
Use std::stod, something like this:
#include <string>
double d = std::stod(cmdBody);
std::istringstream istream(std::string("3.14"));
double d;
istream >> d;
if (!istream.fail())
{
// convertion ok
}
I have a question about unsigned ints.
I would like to convert my unsigned int into a char array. For that I use itoa. The problem is that itoa works properly with ints, but not with unsigned int (the unsigned int is treaded as a normal int).
How should I convert unsigned int into a char array?
Thanks in advance for help!
using stringstream is a common approach:
#include<sstream>
...
std::ostringstream oss;
unsigned int u = 598106;
oss << u;
printf("char array=%s\n", oss.str().c_str());
Update since C++11 there is std::to_string() method -:
#include<string>
...
unsigned int u = 0xffffffff;
std::string s = std::to_string(u);
You can simply Make your own function like this one :
Code Link On Ideone using OWN Function
#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main()
{
unsigned int num,l,i;
cin>>num;
l = log10(num) + 1; // Length of number like if num=123456 then l=6.
char* ans = new char[l+1];
i = l-1;
while(num>0 && i>=0)
{
ans[i--]=(char)(num%10+48);
num/=10;
}
ans[l]='\0';
cout<<ans<<endl;
delete ans;
return 0;
}
You can also use the sprintf function (standard in C)
sprintf(str, "%d", a); //a is your number ,str will contain your number as string
Code Link On Ideone Using Sprintf
_wtoi when can't convert input, so input isn't integer, returns zero. But the same time input can be zero. Is it a way to determine if there was wrong input or zero?
This is C++, you should be using stringstream to do your conversion:
#include <iostream>
#include <sstream>
int main()
{
using namespace std;
string s = "1234";
stringstream ss;
ss << s;
int i;
ss >> i;
if (ss.fail( ))
{
throw someWeirdException;
}
cout << i << endl;
return 0;
}
A cleaner and easier solution exists with boost's lexical_cast:
#include <boost/lexcal_cast.hpp>
// ...
std::string s = "1234";
int i = boost::lexical_cast<int>(s);
If you insist on using C, sscanf can do this cleanly.
const char *s = "1234";
int i = -1;
if(sscanf(s, "%d", &i) == EOF)
{
//error
}
You can also use strtol with the caveat that it requires a little thinking. Yes, it'll return zero for both strings evaluating to zero and for error, but it also has an (optional) parameter endptr which will point to the next character after the numeric that's been converted:
const char *s = "1234";
const char *endPtr;
int i = strtol(s, &endPtr, 10);
if (*endPtr != NULL) {
//error
}
I am new in c++ programming and I have been trying to convert from const char* to unsigned int with no luck.
I have a:
const char* charVar;
and i need to convert it to:
unsigned int uintVar;
How can it be done in C++?
Thanks
#include <iostream>
#include <sstream>
const char* value = "1234567";
stringstream strValue;
strValue << value;
unsigned int intValue;
strValue >> intValue;
cout << value << endl;
cout << intValue << endl;
Output:
1234567
1234567
What do you mean by convert?
If you are talking about reading an integer from the text, then you have several options.
Boost lexical cast: http://www.boost.org/doc/libs/1_44_0/libs/conversion/lexical_cast.htm
String stream:
const char* x = "10";
int y;
stringstream s(x);
s >> y;
Or good old C functions atoi() and strtol()
If you really want to convert a pointer to a constant character into an unsigned int then you should use in c++:
const char* p;
unsigned int i = reinterpret_cast<unsigned int>( p );
This converts the address to which the pointer points to into an unsigned integer.
If you want to convert the content to which the pointer points to into an unsigned int you should use:
const char* p;
unsigned int i = static_cast<unsigned int>( *p );
If you want to get an integer from a string, and hence interpret the const char* as a pointer to a const char array, you can use one of the solutions mentioned above.
The C way:
#include <stdlib.h>
int main() {
const char *charVar = "16";
unsigned int uintVar = 0;
uintVar = atoi(charVar);
return 0;
}
The C++ way:
#include <sstream>
int main() {
istringstream myStream("16");
unsigned int uintVar = 0;
myStream >> uintVar;
return 0;
}
Notice that in neither case did I check the return code of the conversion to make sure it actually worked.
In C this can be done using atoi which is also available to C++ via cstdlib.
I usually use this generic function to convert a string into "anything":
#include <sstream>
// Convert string values into type T results.
// Returns false in case the conversion fails.
template <typename T>
bool getValueFromString( const std::string & value, T & result )
{
std::istringstream iss( value );
return !( iss >> result ).fail();
}
just use it as in:
int main()
{
const char * a_string = "44";
unsigned int an_int;
bool success;
// convert from const char * into unsigned int
success = getValueFromString( a_string, an_int );
// or any other generic convertion
double a;
int b;
float c;
// conver to into double
success = getValueFromString( "45", a );
// conve rto into int
success = getValueFromString( "46", b );
// conver to into float
success = getValueFromString( "47.8", c );
}
atoi function will convert const char* to int, which can be implicitly converted to unsigned. This won't work for large integers that don't fit in int.
A more C++-ish way is to use strings and streams
#include <sstream>
#include <string>
int main()
{
std::string strVar;
unsigned uintVar;
std::istringstream in(strVar);
in >> uintVar;
}
An easier but nonstandard way would be to use boost's lexical cast.
HTH
So I know this is old but thought I would provide a more efficient way of doing this that will give you some flexibility on what you want as a base is.
#include<iostream>
unsigned long cstring_to_ul(const char* str, char** end = nullptr, int base = 10)
{
errno = 0; // Used to see if there was success or failure
auto ul = strtoul(str, end, base);
if(errno != ERANGE)
{
return ul;
}
return ULONG_MAX;
}
What this will do is create a wrapper around the method strtoul(const char* nptr, char** endptr, int base) method from C. For more information on this function you can read the description from the man page here https://linux.die.net/man/3/strtoul
Upon failure you will have errno = ERANGE, which will allow you to do a check after calling this function along with the value being ULONG_MAX.
An example of using this can be as follows:
int main()
{
unsigned long ul = cstring_to_ul("3284201");
if(errno == ERANGE && ul == ULONG_MAX)
{
std::cout << "Input out of range of unsigned long.\n";
exit(EXIT_FAILURE);
}
std::cout << "Output: " << ul << "\n";
}
This will give the output
Output: 3284201
Try in this way
#include<iostream>
#include <typeinfo> //includes typeid
using namespace std;
int main(){
char a = '3';
int k = 3;
const char* ptr = &a;
cout << typeid(*ptr).name() << endl; //prints the data type c = char
cout << typeid(*ptr-'0').name() << endl; //prints the data type i = integer
cout << *ptr-'0' << endl;
return 0;
}
Without more information there is no way to properly answer this question. What are you trying to convert exactly? If charVar is an ascii representation of the string, then you can do like others have suggested and use stringstreams, atoi, sscanf, etc.
If you want the actual value pointed to by charVar, then instead you'd want something like:
intValue = (unsigned int)(*charVal);
Or if charVal is the pointer to the first byte of an unsigned integer then:
intValue = *((unsigned int*)(charVal));
const char* charVar = "12345";
unsigned int uintVar;
try {
uintVar = std::stoi( std::string(charVar) );
}
catch(const std::invalid_argument& e) {
std::cout << "Invalid Arg: " << e.what() << endl;
}
catch(const std::out_of_range& e) {
std::cout << "Out of range: " << e.what() << endl;
}
You can also use strtoul or _tcstoul to get unsigned long value from const char* and then cast the value to unsigned int.
http://msdn.microsoft.com/en-us/library/5k9xb7x1(v=vs.71).aspx
const char* charVar = "1864056953";
unsigned int uintVar = 0;
for (const char* it = charVar; *it != 0; *it++){
if ((*it < 48) || (*it > 57)) break; // see ASCII table
uintVar *= 10; // overflow may occur
uintVar += *it - 48; //
}
std::cout << uintVar << std::endl;
std::cout << charVar << std::endl;