Archive for December 10th, 2013

Replace Non-Alphanumeric Characters in a C++ String

I needed to replace the non-alphanumeric characters in a std::string. While the Java String class has the replace() and replaceAll() methods for doing this, the std::string class has no such utility methods. Instead you can use the std::replace_if function from the Standard Template Library. Here’s some example code:

#include <iostream>
#include <string>
#include <algorithm>

int isNotAlphaNum(char c)
{
        return !std::isalnum(c);
}

int main(int argc, char* argv[])
{
        std::string s1 = "some/string/with*/nonalpha/characters+1";

        std::cout << s1 << " : ";
        std::replace_if(s1.begin(), s1.end(), isNotAlphaNum, ' ');
        std::cout << s1 << std::endl;

        return 0;
}

The third parameter of the replace_if() function is a pointer to a function that performs the desired check and returns either true or false if the input satisfies the condition. The last parameter is the character to replace the matched character, in this case a space.

This program produces the following:

$ ./replace.exe 
some/string/with*/nonalpha/characters+1
some string with  nonalpha characters 1

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Tuesday, December 10th, 2013 Cpp, Programming, Tips and Tricks No Comments

Convert C++ String to Lower Case (or Upper Case)

I don’t usually need to convert string case in C++ so when the need comes up I’ve usually forgotten how to do it and have to Google.

While the Java String class has toLowerCase() and toUpperCase(), C++ std::string does not have such a utility method. Instead, you need to use the std::transform() function. Here’s some example code:

#include <iostream>
#include <string>
#include <utility>

int main(int argc, char* argv[])
{
        std::string s1 = "lowertoupper";
        std::string s2 = "UPPERTOLOWER";

        std::cout << s1 << " : ";
        std::transform(s1.begin(), s1.end(), s1.begin(), ::toupper);
        std::cout << s1 << std::endl;

        std::cout << s2 << " : ";
        std::transform(s2.begin(), s2.end(), s2.begin(), ::tolower);
        std::cout << s2 << std::endl;

        return 0;
}

Produces the following:

$ ./case.exe 
lowertoupper : LOWERTOUPPER
UPPERTOLOWER : uppertolower

Note that while the Java toUpperCase() and toLowerCase() methods do not modify the original string, the std::transform function does.

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Tuesday, December 10th, 2013 Cpp, Programming, Tips and Tricks No Comments