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Thinking in C++ Vol 2 - Practical Programming
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Finding first/last of a set of characters

The find_first_of( ) and find_last_of( ) member functions can be conveniently put to work to create a little utility that will strip whitespace characters from both ends of a string. Notice that it doesn t touch the original string, but instead returns a new string:

//: C03:Trim.h
// General tool to strip spaces from both ends.
#ifndef TRIM_H
#define TRIM_H
#include <string>
#include <cstddef>
inline std::string trim(const std::string& s) {
if(s.length() == 0)
return s;
std::size_t beg = s.find_first_not_of(" \a\b\f\n\r\t\v");
std::size_t end = s.find_last_not_of(" \a\b\f\n\r\t\v");
if(beg == std::string::npos) // No non-spaces
return "";
return std::string(s, beg, end - beg + 1);
#endif // TRIM_H ///:~

The first test checks for an empty string; in that case, no tests are made, and a copy is returned. Notice that once the end points are found, the string constructor builds a new string from the old one, giving the starting count and the length.

Testing such a general-purpose tool needs to be thorough:

//: C03:TrimTest.h
#ifndef TRIMTEST_H
#define TRIMTEST_H
#include "Trim.h"
#include "../TestSuite/Test.h"
class TrimTest : public TestSuite::Test {
enum {NTESTS = 11};
static std::string s[NTESTS];
void testTrim() {
test_(trim(s[0]) == "abcdefghijklmnop");
test_(trim(s[1]) == "abcdefghijklmnop");
test_(trim(s[2]) == "abcdefghijklmnop");
test_(trim(s[3]) == "a");
test_(trim(s[4]) == "ab");
test_(trim(s[5]) == "abc");
test_(trim(s[6]) == "a b c");
test_(trim(s[7]) == "a b c");
test_(trim(s[8]) == "a \t b \t c");
test_(trim(s[9]) == "");
test_(trim(s[10]) == "");
void run() {
#endif // TRIMTEST_H ///:~
//: C03:TrimTest.cpp {O}
#include "TrimTest.h"
// Initialize static data
std::string TrimTest::s[TrimTest::NTESTS] = {
" \t abcdefghijklmnop \t ",
"abcdefghijklmnop \t ",
" \t abcdefghijklmnop",
"a", "ab", "abc", "a b c",
" \t a b c \t ", " \t a \t b \t c \t ",
"\t \n \r \v \f",
"" // Must also test the empty string
}; ///:~
//: C03:TrimTestMain.cpp
//{L} ../TestSuite/Test TrimTest
#include "TrimTest.h"
int main() {
TrimTest t;;
} ///:~

In the array of strings, you can see that the character arrays are automatically converted to string objects. This array provides cases to check the removal of spaces and tabs from both ends, as well as ensuring that spaces and tabs are not removed from the middle of a string.

Thinking in C++ Vol 2 - Practical Programming
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire