Merge pull request #15 from DoctorLai/ranges-find-in-vector-string

Different ways to find an element in a vector string

Author: doctorlai-msrc

README.md

@@ -26,6 +26,8 @@ Examples include (and will expand to):
 * Parallelism
     * [parallel-transform](./parallel-transform/)
 * Performance‑oriented C++ idioms
+* STL and ranges:
+    * [ranges-find-in-vector-string](./ranges-find-in-vector-string/)
 * Algorithms
     * [integer-factorization](./integer-factorization/)
     * Encoding

map-with-unknown-key/main.cpp

@@ -3,17 +3,48 @@ What happens if you access an unknown key in the std::map, std::unordered_map?
 */
 #include <iostream>
 #include <map>
+#include <unordered_map>
 #include <string>
-#include <format>
 #include <print>
+#include <cassert>
 
 int
 main()
 {
+    // Example with std::map value type int
     std::map<std::string, int> my_map;
     std::print("Accessing unknown key 'unknown_key' in std::map:\n");
     int value = my_map["unknown_key"];
     std::print("Value: {}\n", value);                         // Should print 0, as default-constructed int is 0
     std::print("Map size after access: {}\n", my_map.size()); // Should print 1
+    assert(value == 0);                                       // Default-constructed int is 0
+    assert(my_map.size() == 1);                               // The map now contains one entry for 'unknown_key'
+
+    // Example with std::unordered_map value type int
+    std::unordered_map<std::string, int> my_unordered_map;
+    std::print("Accessing unknown key 'unknown_key' in std::unordered_map:\n");
+    int unordered_value = my_unordered_map["unknown_key"];
+    std::print("Value: {}\n", unordered_value);                                   // Should print 0
+    std::print("Unordered map size after access: {}\n", my_unordered_map.size()); // Should print 1
+    assert(unordered_value == 0);                                                 // Default-constructed int is 0
+    assert(my_unordered_map.size() == 1); // The unordered_map now contains one entry for 'unknown_key'
+
+    // Example with std::map value type std::string
+    std::map<std::string, std::string> my_string_map;
+    std::print("Accessing unknown key 'unknown_key' in std::map with string values:\n");
+    std::string str_value = my_string_map["unknown_key"];
+    std::print("Value: '{}'\n", str_value);                          // Should print empty string
+    std::print("Map size after access: {}\n", my_string_map.size()); // Should print 1
+    assert(str_value.empty());                                       // Default-constructed string is empty
+    assert(my_string_map.size() == 1);                               // The map now contains one entry for
+
+    // Example with std::unordered_map value type std::string
+    std::unordered_map<std::string, std::string> my_string_unordered_map;
+    std::print("Accessing unknown key 'unknown_key' in std::unordered_map with string values:\n");
+    std::string str_unordered_value = my_string_unordered_map["unknown_key"];
+    std::print("Value: '{}'\n", str_unordered_value);                                    // Should print empty string
+    std::print("Unordered map size after access: {}\n", my_string_unordered_map.size()); // Should print 1
+    assert(str_unordered_value.empty());         // Default-constructed string is empty
+    assert(my_string_unordered_map.size() == 1); // The unordered_map now contains one entry for 'unknown_key'
     return 0;
 }

ranges-find-in-vector-string/Makefile

@@ -0,0 +1,31 @@
+# pull in shared compiler settings
+include ../common.mk
+
+# per-example flags
+# CXXFLAGS += -pthread
+
+## get it from the folder name
+TARGET := $(notdir $(CURDIR))
+## all *.cpp files in this folder
+SRCS   := $(wildcard *.cpp)
+OBJS   := $(SRCS:.cpp=.o)
+
+all: $(TARGET)
+
+$(TARGET): $(OBJS)
+	$(CXX) $(CXXFLAGS) -o $@ $^
+
+%.o: %.cpp
+	$(CXX) $(CXXFLAGS) -c $< -o $@
+
+run: $(TARGET)
+	./$(TARGET) $(ARGS)
+
+clean:
+	rm -f $(OBJS) $(TARGET)
+
+# Delegates to top-level Makefile
+check-format:
+	$(MAKE) -f ../Makefile check-format DIR=$(CURDIR)
+
+.PHONY: all clean run check-format

ranges-find-in-vector-string/main.cpp

@@ -0,0 +1,133 @@
+/**
+This demonstrates different ways to find an element in a vector of strings
+*/
+#include <iostream>
+#include <vector>
+#include <string>
+#include <print>
+#include <cassert>
+#include <ranges>
+#include <algorithm>
+
+int
+main()
+{
+    std::vector<std::string> vec = {"apple", "banana", "cherry", "date", "elderberry"};
+    std::string target = "cherry";
+
+    // Method 1: Using a loop
+    bool found = false;
+    for (size_t i = 0; i < vec.size(); ++i) {
+        if (vec[i] == target) {
+            std::print("loop: Found '{}' using loop at index {}\n", target, i);
+            found = true;
+            break;
+        }
+    }
+    if (!found) {
+        std::print("loop: '{}' not found using loop\n", target);
+    }
+
+    // Method 2: Using std::find_if with a lambda
+    auto it_if = std::find_if(vec.begin(), vec.end(), [&target](const std::string& s) { return s == target; });
+    if (it_if != vec.end()) {
+        std::print(
+            "std::find_if: Found '{}' using std::find_if at index {}\n", target, std::distance(vec.begin(), it_if));
+    } else {
+        std::print("std::find_if: '{}' not found using std::find_if\n", target);
+    }
+
+    // Method 3: Using std::find
+    auto it = std::find(vec.begin(), vec.end(), target);
+    if (it != vec.end()) {
+        std::print("std::find: Found '{}' using std::find at index {}\n", target, std::distance(vec.begin(), it));
+    } else {
+        std::print("std::find: '{}' not found using std::find\n", target);
+    }
+
+    // Method 4: std::count (pre C++20)
+    auto count_std = std::count(vec.begin(), vec.end(), target);
+    std::print("std::count: Vector contains '{}' {} time(s) using std::count\n", target, count_std);
+
+    // Method 5: std::count_if (pre C++20)
+    auto count_if_std = std::count_if(vec.begin(), vec.end(), [&target](const std::string& s) { return s == target; });
+    std::print("std::count_if: Vector contains '{}' {} time(s) using std::count_if\n", target, count_if_std);
+
+    // Method 6: std::any_of
+    bool any_of_std = std::any_of(vec.begin(), vec.end(), [&target](const std::string& s) { return s == target; });
+    if (any_of_std) {
+        std::print("std::any_of: Vector contains '{}' using std::any_of\n", target);
+    } else {
+        std::print("std::any_of: Vector does not contain '{}' using std::any_of\n", target);
+    }
+
+    // Method 7: Using std::ranges::find (C++20)
+    auto range_it = std::ranges::find(vec, target);
+    if (range_it != vec.end()) {
+        std::print(
+            "std::ranges::find: Found '{}' using std::ranges::find at index {}\n",
+            target,
+            std::distance(vec.begin(), range_it));
+    } else {
+        std::print("std::ranges::find: '{}' not found using std::ranges::find\n", target);
+    }
+
+    // Method 8: Using std::ranges::find_if with a lambda (C++20)
+    auto range_it_if = std::ranges::find_if(vec, [&target](const std::string& s) { return s == target; });
+    if (range_it_if != vec.end()) {
+        std::print(
+            "std::ranges::find_if: Found '{}' using std::ranges::find_if at index {}\n",
+            target,
+            std::distance(vec.begin(), range_it_if));
+    } else {
+        std::print("std::ranges::find_if: '{}' not found using std::ranges::find_if\n", target);
+    }
+
+    // Method 9: std::ranges::contains (C++23)
+    auto contains = std::ranges::contains(vec, target);
+    if (contains) {
+        std::print("std::ranges::contains: Vector contains '{}' using std::ranges::contains\n", target);
+    } else {
+        std::print("std::ranges::contains: Vector does not contain '{}' using std::ranges::contains\n", target);
+    }
+
+    // Method 10: std::ranges::any_of (C++20)
+    bool any_of = std::ranges::any_of(vec, [&target](const std::string& s) { return s == target; });
+    if (any_of) {
+        std::print("std::ranges::any_of: Vector contains '{}' using std::ranges::any_of\n", target);
+    } else {
+        std::print("std::ranges::any_of: Vector does not contain '{}' using std::ranges::any_of\n", target);
+    }
+
+    // Method 11: std::ranges::count (C++20)
+    auto count = std::ranges::count(vec, target);
+    std::print("std::ranges::count: Vector contains '{}' {} time(s) using std::ranges::count\n", target, count);
+
+    // Method 12: std::ranges::count_if (C++20)
+    auto count_if = std::ranges::count_if(vec, [&target](const std::string& s) { return s == target; });
+    std::print(
+        "std::ranges::count_if: Vector contains '{}' {} time(s) using std::ranges::count_if\n", target, count_if);
+
+    // Method 13: via std::ranges::views (C++20)
+    auto view = vec | std::ranges::views::filter([&target](const std::string& s) { return s == target; });
+    for (const auto& s : view) {
+        std::print("std::ranges::views::filter: Found '{}' using std::ranges::views::filter\n", s);
+    }
+
+    // Assertions to verify correctness
+    assert(it != vec.end() && *it == target);
+    assert(found);
+    assert(range_it != vec.end() && *range_it == target);
+    assert(it_if != vec.end() && *it_if == target);
+    assert(range_it_if != vec.end() && *range_it_if == target);
+    assert(contains);
+    assert(any_of);
+    assert(count == 1);
+    assert(count_std == 1);
+    assert(count_if == 1);
+    assert(count_if_std == 1);
+    assert(std::ranges::distance(view) == 1);
+    assert(any_of_std);
+
+    return 0;
+}

ranges-find-in-vector-string/tests.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+set -ex
+
+./ranges-find-in-vector-string