Defined in header <cmath>  

float trunc( float arg );  (1)  (since C++11) 
double trunc( double arg );  (2)  (since C++11) 
long double trunc( long double arg );  (3)  (since C++11) 
double trunc( Integral arg );  (4)  (since C++11) 
arg
. double
).arg    floating point value 
If no errors occur, the nearest integer value not greater in magnitude than arg
(in other words, arg
rounded towards zero), is returned.
Errors are reported as specified in math_errhandling.
If the implementation supports IEEE floatingpoint arithmetic (IEC 60559),
arg
is ±∞, it is returned, unmodified arg
is ±0, it is returned, unmodified FE_INEXACT
may be (but isn't required to be) raised when truncating a noninteger finite value.
The largest representable floatingpoint values are exact integers in all standard floatingpoint formats, so this function never overflows on its own; however the result may overflow any integer type (including std::intmax_t
), when stored in an integer variable.
The implicit conversion from floatingpoint to integral types also rounds towards zero, but is limited to the values that can be represented by the target type.
#include <cmath> #include <iostream> int main() { std::cout << std::fixed << "trunc(+2.7) = " << std::trunc(+2.7) << '\n' << "trunc(2.9) = " << std::trunc(2.9) << '\n' << "trunc(0.0) = " << std::trunc(0.0) << '\n' << "trunc(Inf) = " << std::trunc(INFINITY) << '\n'; }
Possible output:
trunc(+2.7) = 2.000000 trunc(2.9) = 2.000000 trunc(0.0) = 0.000000 trunc(Inf) = inf
nearest integer not greater than the given value (function) 

nearest integer not less than the given value (function) 

(C++11)(C++11)(C++11)  nearest integer, rounding away from zero in halfway cases (function) 
C documentation for trunc 
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