Argument Coercion in C/C++

Argument coercion is a feature of function prototypes by which the compiler implicitly converts the datatype of the arguments passed during the function call to match the datatype in the definition of the function.

It follows Argument promotion rules. Therefore a lower datatype maybe converted into a higher datatype but vice-versa is not true. This is because when a higher datatype is converted to a lower datatype it can result into loss or truncation of data.

The Promotion hierarchy for fundamental datatypes in C++ is:

Example: Take for Example the code given below consists of an add function that expects double arguments. But even when integer arguments are passed it works correctly. In case long double arguments are passed the code will give an error.





#include <iostream>
using namespace std;
double add(double a, double b)
    return a + b;
int main()
    // Passing double arguments, as expected
    cout << "Sum = " << add(2.4, 8.5) << endl;
    // Passing int arguments, when double is expected
    // This will lead to Argument Coercion
    cout << "Sum = " << add(16, 18) << endl;
    return 0;


Don’t stop now and take your learning to the next level. Learn all the important concepts of Data Structures and Algorithms with the help of the most trusted course: DSA Self Paced. Become industry ready at a student-friendly price.

My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using or mail your article to See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.