Transformation of std::string

23 July 2014

Why I need this?

In a small project, I need to compare a user input of type std::string with predefined commands, which are case insesnsitive. So I need to convert the string to lower case first.

Is there a method within std::string?

Directly? Noop.

But, there’s only one step forward.

Let’s see.

General algorithm API

In algorithm header, there is a general algorithm API: transform, which can help us achieve the goal.

main.cpp

#include <iostream>

#include <string>
#include <algorithm>

typedef int(*UnaryOperator)(int);

static int minusOne(int x);
static std::string transformFor(const std::string &str, UnaryOperator op);

int main(int argc, char *argv[]) {
    UnaryOperator ops[] = {
        tolower,
        toupper,
        minusOne,
    };

    int n = sizeof(ops) / sizeof(ops[0]);

    for (int i = 1; i < argc; i++) {
        if (i > 1) {
            std::cout << std::endl;
        }

        std::string str = argv[i];
        std::cout << str;

        for (int j = 0; j < n; j++) {
            std::string t = transformFor(str, ops[j]);
            std::cout << "\t->\t" << t << std::endl;
        }
    }

    return 0;
}

int minusOne(int x) {
    return x - 1;
}

std::string transformFor(const std::string &str, UnaryOperator op) {
    std::string t = str;

    transform(str.begin(), str.end(), t.begin(), op);

    return t;
}

Conclusion

As can be seen from the code, arbitrary operation functions can be defined, as minusOne in above code, in the meanwhile make full use of the API without reinvent the wheel, which is the essence of flexibility and reusability.

Programs 8