Searching for a Substring Appearing Multiple Times
How do I handle searching for a substring within a string when the substring can appear multiple times?
To handle searching for a substring that appears multiple times within a string, you can use a loop with the std::string::find() function. This method allows you to locate all occurrences of the substring.
Using a Loop with std::string::find()
Here's an example:
#include <iostream>
#include <string>
int main() {
std::string text = "This is a test."
"This test is only a test.";
std::string target = "test";
std::size_t pos = text.find(target);
while (pos != std::string::npos) {
std::cout << "Found '" << target
<< "' at position " << pos << "\n";
pos = text.find(target, pos + target.length());
}
}Found 'test' at position 10
Found 'test' at position 20
Found 'test' at position 35Explanation
std::string::find()searches for the first occurrence of the substring.- The loop continues searching by updating the position to start just after the last found substring.
- The loop terminates when
std::string::npos(indicating no more occurrences) is returned.
Handling Overlapping Substrings
If the substrings can overlap, adjust the position increment. By incrementing the position by 1, overlapping occurrences are also found:
#include <iostream>
#include <string>
int main() {
std::string text = "aaa";
std::string target = "aa";
std::size_t pos = text.find(target);
while (pos != std::string::npos) {
std::cout << "Found '" << target
<< "' at position " << pos << "\n";
pos = text.find(target, pos + 1);
}
}Found 'aa' at position 0
Found 'aa' at position 1Using Regular Expressions
For more complex search patterns, consider using std::regex:
#include <iostream>
#include <regex>
#include <string>
int main() {
std::string text = "test1 test2 test1 test2";
std::regex pattern("test[0-9]");
auto words_begin = std::sregex_iterator(
text.begin(), text.end(), pattern);
auto words_end = std::sregex_iterator();
for (auto it = words_begin; it != words_end; ++it) {
std::smatch match = *it;
std::cout << "Found '" << match.str()
<< "' at position "
<< match.position() << "\n";
}
}Found 'test1' at position 0
Found 'test2' at position 6
Found 'test1' at position 12
Found 'test2' at position 18Explanation
std::regexallows for complex pattern matching.std::sregex_iteratoris used to iterate through all matches.
By using these methods, you can effectively search for a substring that appears multiple times within a string, handling both non-overlapping and overlapping cases, as well as more complex patterns.
Search Algorithms
An introduction to the 8 main searching algorithms in the C++ standard library, including find(), find_if(), find_if_not(), find_first_of(), adjacent_find(), search_n(), search(), and find_end().