Yesterday I once again stumbled upon whitespace trimming of STL strings: a check was required if the given user input is empty. Where "empty" also means some user-given string containing only spaces. After one hour of unproductive searching for something as simple as a space trimming function, I decided to put the resulting code here for future reference.
The following code snippet contains two versions of the function: in-place trimming and string-copy trimming. I prefer the copy-trimming function because they allow a more functional programming style. The functions only trim spaces, but can be modified by replacing each ' ' with something like " \n\r\t".
#include <string>
static inline void string_trim_left_inplace(std::string &str)
{
str.erase(0, str.find_first_not_of(' '));
}
static inline void string_trim_right_inplace(std::string &str)
{
str.erase(str.find_last_not_of(' ') + 1, std::string::npos);
}
static inline std::string string_trim_left(const std::string &str)
{
std::string::size_type pos = str.find_first_not_of(' ');
if (pos == std::string::npos) return std::string();
return str.substr(pos, std::string::npos);
}
static inline std::string string_trim_right(const std::string &str)
{
std::string::size_type pos = str.find_last_not_of(' ');
if (pos == std::string::npos) return std::string();
return str.substr(0, pos + 1);
}
static inline std::string string_trim(const std::string& str)
{
std::string::size_type pos1 = str.find_first_not_of(' ');
if (pos1 == std::string::npos) return std::string();
std::string::size_type pos2 = str.find_last_not_of(' ');
if (pos2 == std::string::npos) return std::string();
return str.substr(pos1 == std::string::npos ? 0 : pos1,
pos2 == std::string::npos ? (str.length() - 1) : (pos2 - pos1 + 1));
}
static inline void string_trim_inplace(std::string& str)
{
std::string::size_type pos = str.find_last_not_of(' ');
if(pos != std::string::npos) {
str.erase(pos + 1);
pos = str.find_first_not_of(' ');
if(pos != std::string::npos) str.erase(0, pos);
}
else
str.erase(str.begin(), str.end());
}
#include <assert.h>
// Test the functions above
int main()
{
// string-copy functions
assert( string_trim_left(" abc ") == "abc " );
assert( string_trim_left("abc ") == "abc " );
assert( string_trim_left(" ") == "" );
assert( string_trim_right(" abc ") == " abc" );
assert( string_trim_right(" abc") == " abc" );
assert( string_trim_right(" ") == "" );
assert( string_trim(" abc ") == "abc" );
assert( string_trim("abc ") == "abc" );
assert( string_trim(" abc") == "abc" );
assert( string_trim(" ") == "" );
// in-place functions
std::string str1 = " abc ";
std::string str2 = "abc ";
std::string str3 = " ";
string_trim_left_inplace(str1);
string_trim_left_inplace(str2);
string_trim_left_inplace(str3);
assert( str1 == "abc " );
assert( str2 == "abc " );
assert( str3 == "" );
str1 = " abc ";
str2 = " abc";
str3 = " ";
string_trim_right_inplace(str1);
string_trim_right_inplace(str2);
string_trim_right_inplace(str3);
assert( str1 == " abc" );
assert( str2 == " abc" );
assert( str3 == "" );
str1 = " abc ";
str2 = " abc";
str3 = "abc ";
std::string str4 = " ";
string_trim_inplace(str1);
string_trim_inplace(str2);
string_trim_inplace(str3);
string_trim_inplace(str4);
assert( str1 == "abc" );
assert( str2 == "abc" );
assert( str3 == "abc" );
assert( str4 == "" );
return 0;
}
