What are the different techniques used to convert float type of data to integer in C++?
#include <iostream> using namespace std; struct database { int id, age; float salary; }; int main() { struct database employee; employee.id = 1; employee.age = 23; employee.salary = 45678.90; /* How can i print this value as an integer (with out changing the salary data type in the declaration part) ? */ cout << endl << employee.id << endl << employee. age << endl << employee.salary << endl; return 0; } What you are looking for is 'type casting'. typecasting (putting the type you know you want in brackets) tells the compiler you know what you are doing and are cool with it. The old way that is inherited from C is as follows.
float var_a = 9.99; int var_b = (int)var_a; // var_b = 9 If you had only tried to write
int var_b = var_a; You would have got a warning that you can't implicitly (automatically) convert a float to an int, as you lose the decimal.
This is referred to as the old way as C++ offers a superior alternative, 'static cast'; this provides a much safer way of converting from one type to another. The equivalent method would be (and the way you should do it)
float var_x = 9.99; int var_y = static_cast<int>(var_x); // var_y = 9 This method may look a bit more long winded, but it provides much better handling for situations such as accidentally requesting a 'static cast' on a type that cannot be converted. For more information on the why you should be using static cast, see this question.
NaN, how could the above "old way" code result in an unconvertible type? We know in advance that var_a is a float.Normal way is to:
float pi = 3.1415; int i = static_cast<int>(f); // i = 3 Always rounds down:
float f = 3.999; int n = static_cast<int>(f); // n = 3 
Size of some float types may exceed the size of int. This example shows a safe conversion of any float type to int using the int safeFloatToInt(const FloatType &num); function:
#include <iostream> #include <limits> using namespace std; template <class FloatType> int safeFloatToInt(const FloatType &num) { //check if float fits into integer if ( numeric_limits<int>::digits < numeric_limits<FloatType>::digits) { // check if float is smaller than max int if( (num < static_cast<FloatType>( numeric_limits<int>::max())) && (num > static_cast<FloatType>( numeric_limits<int>::min())) ) { return static_cast<int>(num); //safe to cast } else { cerr << "Unsafe conversion of value:" << num << endl; //NaN is not defined for int return the largest int value return numeric_limits<int>::max(); } } else { //It is safe to cast return static_cast<int>(num); } } int main(){ double a=2251799813685240.0; float b=43.0; double c=23333.0; //unsafe cast cout << safeFloatToInt(a) << endl; cout << safeFloatToInt(b) << endl; cout << safeFloatToInt(c) << endl; return 0; } Result:
Unsafe conversion of value:2.2518e+15 2147483647 43 23333 
numeric_limits<int>::max() could get rounded to a slightly larger float value, and then if you pass exactly this larger value to safeFloatToInt it will pass the checks (because it uses strict inequalities) but still be undefined?
safeFloatToInt(b) with float b = std::numeric_limits<int>::max() - x; will cause UB for 0 < x < 64.Check out the boost NumericConversion library. It will allow to explicitly control how you want to deal with issues like overflow handling and truncation.
One thing I want to add. Sometimes, there can be precision loss. You may want to add some epsilon value first before converting. Not sure why that works... but it work.
int someint = (somedouble+epsilon); 
5 for instance but the computer stores it as 4.999..., so if you cast to int without the epsilon it will unintentionally become 4.I know this is an old question, but hope my answer can help. Here what I use in for my microcontroller:
float temperature = 31.14 float humidity = 66.70 int intTemperature = static_cast<int>(round(temperature)); int intHumidity = static_cast<int>(round(humidity)); 
This is one way to convert IEEE 754 float to 32-bit integer if you can't use floating point operations. It has also a scaler functionality to include more digits to the result. Useful values for scaler are 1, 10 and 100.
#define EXPONENT_LENGTH 8 #define MANTISSA_LENGTH 23 // to convert float to int without floating point operations int ownFloatToInt(int floatBits, int scaler) { int sign = (floatBits >> (EXPONENT_LENGTH + MANTISSA_LENGTH)) & 1; int exponent = (floatBits >> MANTISSA_LENGTH) & ((1 << EXPONENT_LENGTH) - 1); int mantissa = (floatBits & ((1 << MANTISSA_LENGTH) - 1)) | (1 << MANTISSA_LENGTH); int result = mantissa * scaler; // possible overflow exponent -= ((1 << (EXPONENT_LENGTH - 1)) - 1); // exponent bias exponent -= MANTISSA_LENGTH; // modify exponent for shifting the mantissa if (exponent <= -(int)sizeof(result) * 8) { return 0; // underflow } if (exponent > 0) { result <<= exponent; // possible overflow } else { result >>= -exponent; } if (sign) result = -result; // handle sign return result; }