panthema / 2007 / 0602-StdString-Upper-Lower

C++ Code Snippet - In-Place and String-Copy Uppercase/Lowercase Conversion of STL Strings

Posted on 2007-06-02 13:22 by Timo Bingmann at Permlink with 2 Comments. Tags: c++ code-snippet

This post completes the small C++ function collection of simple STL string manipulations. The following code snippet shows simple locale-unware uppercase and lowercase conversion functions using tolower and toupper. Nothing revolutionary; I'm just misusing this weblog as a code-paste dump for reuseable code.

Sometimes it is better to have a case-insensitive string class. More about ci_string can be found at Guru of the Week (GotW) #29: Case-Insensitive Strings.

#include <string>
#include <cctype>

// functionals for std::transform with correct signature
static inline char string_toupper_functional(char c)
    return std::toupper(c);

static inline char string_tolower_functional(char c)
    return std::tolower(c);

static inline void string_upper_inplace(std::string &str)
    std::transform(str.begin(), str.end(), str.begin(), string_toupper_functional);

static inline void string_lower_inplace(std::string &str)
    std::transform(str.begin(), str.end(), str.begin(), string_tolower_functional);

static inline std::string string_upper(const std::string &str)
    std::string strcopy(str.size(), 0);
    std::transform(str.begin(), str.end(), strcopy.begin(), string_toupper_functional);
    return strcopy;

static inline std::string string_lower(const std::string &str)
    std::string strcopy(str.size(), 0);
    std::transform(str.begin(), str.end(), strcopy.begin(), string_tolower_functional);
    return strcopy;
#include <assert.h>

// Test the functions above
int main()
    // string-copy functions
    assert( string_upper(" aBc ") == " ABC " );
    assert( string_lower(" AbCdEfG ") == " abcdefg " );

    // in-place functions
    std::string str1 = "  aBc  ";
    std::string str2 = "AbCdEfGh ";


    assert( str1 == "  ABC  " );
    assert( str2 == "abcdefgh " );

    return 0;

Comment by fdv1 at 2007-12-19 14:35 UTC
Hi Timo, Thanks for your example of Flex Bison C++ Unless I'm wrong what you provide in this section is already implemeted in : Boost String Algorithms Library cheers François
Comment by Timo at 2007-12-20 14:19 UTC
Yes, this is nothing new or innovative. The Boost.String library is way more flexible and includes many more algorithms. Nevertheless these are the code snippets I copy into programs, when I don't want to include the huge Boost library and just want plain ASCII case-conversions.
Post Comment
E-Mail or Homepage:

URLs (http://...) are displayed, e-mails are hidden and used for Gravatar.

Many common HTML elements are allowed in the text, but no CSS style.
RSS 2.0 Weblog Feed Atom 1.0 Weblog Feed Valid XHTML 1.1 Valid CSS (2.1)
Copyright 2005-2017 Timo Bingmann - Impressum