How to Call a C Function by Its Name Stored in a String?

Calling a Function by Its Name (std::string) in C

In C , the question of calling a function by its name stored in a string has arisen. While a basic approach involving conditional statements is known, simpler alternatives have been sought.

Basic Approach

A straightforward method involves using a series of if-else statements to match the function name with the corresponding function pointer. This approach is illustrated below:

<code class="cpp">int function_1(int i, int j) { return i*j; }
int function_2(int i, int j) { return i/j; }

int callFunction(int i, int j, string function) {
    if(function == "function_1") {
        return function_1(i, j);
    } else if(function == "function_2") {
        return function_2(i, j);
    } ...
    return function_1(i, j);
}</code>

Proposed Alternative

The new approach aims to simplify the calling process by utilizing an std::map to map function names to function pointers. For functions with identical prototypes, this technique can provide a more concise solution:

<code class="cpp">#include <map>

typedef int (*FnPtr)(int, int);

int add(int i, int j) { return i+j; }
int sub(int i, int j) { return i-j; }

int main() {
    std::map<std::string, FnPtr> myMap;
    myMap["add"] = add;
    myMap["sub"] = sub;

    std::string s("add");
    int res = myMap[s](2,3);
    std::cout << res;
}</code>

This approach utilizes the myMap[s](2,3) syntax, which retrieves the function pointer mapped to the string s and invokes the corresponding function with the provided arguments. The example shown calculates and outputs 5 as the result of the "add" function call.

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