trunc() , truncf() , truncl() in C language

In C, the trunc(), truncf(), and truncl() functions are used to truncate floating-point values, removing the fractional part and returning only the integer portion. These functions are part of the math.h library and are available in C99 and later standards.

Installation: These functions require C99 or later. Compile with gcc -std=c99 -lm to link the math library.

Syntax

double trunc(double x);
float truncf(float x);
long double truncl(long double x);

Parameters

• x − The floating-point value to be truncated

Return Value

Returns the truncated value (integer part) as the same data type as the input parameter.

Example 1: Using trunc() Function

The trunc() function works with double type values ?

#include <stdio.h>
#include <math.h>

int main() {
    double x = 53.26;
    double y = -75.86;
    double a = trunc(x);
    double b = trunc(y);
    
    printf("Original: %.2lf, Truncated: %.2lf<br>", x, a);
    printf("Original: %.2lf, Truncated: %.2lf<br>", y, b);
    
    return 0;
}

Original: 53.26, Truncated: 53.00
Original: -75.86, Truncated: -75.00

Example 2: Using truncf() Function

The truncf() function works with float type values ?

#include <stdio.h>
#include <math.h>

int main() {
    float x = 53.26f;
    float y = -75.86f;
    float a = truncf(x);
    float b = truncf(y);
    
    printf("Original: %.2f, Truncated: %.2f<br>", x, a);
    printf("Original: %.2f, Truncated: %.2f<br>", y, b);
    
    return 0;
}

Original: 53.26, Truncated: 53.00
Original: -75.86, Truncated: -75.00

Example 3: Using truncl() Function

The truncl() function works with long double type values for higher precision ?

#include <stdio.h>
#include <math.h>

int main() {
    long double x = 53547.55555555555L;
    long double y = -78547.55555555523L;
    long double a = truncl(x);
    long double b = truncl(y);
    
    printf("Original: %.5Lf, Truncated: %.5Lf<br>", x, a);
    printf("Original: %.5Lf, Truncated: %.5Lf<br>", y, b);
    
    return 0;
}

Original: 53547.55556, Truncated: 53547.00000
Original: -78547.55556, Truncated: -78547.00000

Key Points

• These functions always truncate towards zero (not towards negative infinity)
• For positive numbers: trunc(3.7) returns 3.0
• For negative numbers: trunc(-3.7) returns -3.0
• The return type matches the input parameter type

Conclusion

The trunc() family functions provide a simple way to remove fractional parts from floating-point numbers. They work consistently across different data types and always truncate towards zero, making them useful for converting floating-point values to integers.