How to Create a Vector of Strings in C++

As an experienced C++ developer, vectors are one of my most used standard library data structures. Combined with strings, they provide a versatile container for manipulating text data.

In this comprehensive guide, I‘ll cover everything you need to know about building applications with C++ vectors holding strings, including:

• Initialization syntax and constructors
• Inserting, accessing and erasing elements
• Sorting, comparison and custom string classes
• Passing string vectors between functions
• Thread safety considerations
• Code examples for joining, streaming vectors
• Pros and cons relative to other containers
• Best practices for optimal usage

Follow along for 2600+ words on mastering this fundamental C++ topic.

Overview of Vectors

Vectors serve as dynamically sizable arrays. Unlike regular C arrays, vectors handle memory management automatically. Elements can be inserted or removed efficiently from any location, with minimal impact on the rest of the data.

The elements of a vector are stored contiguously, allowing constant time indexed access using operator[]. This makes vectors ideal for random access.

Internally, vectors typically allocate more memory than they initially need, allowing some growth before reallocation is necessary. The capacity() method returns their total allocated space.

Vectors excel at data access, but inserting/erasing anywhere but the end carries some overhead. Operations like push_back() that append to the end are extremely fast.

Compared to other containers like lists and dequeues, vectors have the advantage of contiguous data for cache efficiency. The tradeoff is less efficient atomic modification in the middle of the sequence.

Overall, vectors are highly versatile and usage is widespread. Their dynamic nature coupled with fast indexing suits them well to string manipulation.

Including the Right Headers

To work with vectors and strings, be sure to include their respective standard library headers:

#include <vector>
#include <string>

The vector header contains the vector class template and supporting functionality.

The string header contains the string class for rich text manipulation.

For convenience, I also typically import the entire standard namespace:

using namespace std;

This allows referring to vectors and strings without the std:: prefix. But an even better practice is to import just the specific components needed:

using std::vector;
using std::string;

Either method eliminates verbosity without polluting your custom namespaces.

Constructing a Vector of Strings

Here is how to declare a vector to contain strings:

vector<string> myStrings;

The template argument specifies the element type.

To initialize strings upon construction:

vector<string> myStrings {"first", "second"}; 

This leverages C++11 uniform initialization and initializer lists.

Or similarly in the constructor:

vector<string> myStrings(2);
myStrings[0] = "first; 
myStrings[1] = "second";

This sets an initial capacity of 2 elements.

Always initialize vectors this way when you know the size upfront, to avoid reallocations as it grows.

Adding Elements to a Vector

There are a few good options to insert new strings into an existing vector:

Push Back

This appends to the end of the vector:

myStrings.push_back("third"); 

Push back is ideal when order does not matter. Appending does not invalidate existing references or iterators.

Insert

To insert at a specific position:

myStrings.insert(myStrings.begin() + 1, "another");

Insert takes an iterator position to handle insertion before the element at that location.

All iterators and references after the insertion point remain valid. But performance degrades as more elements preceed it.

Emplace / Emplace Back

Constructs an element in-place:

myStrings.emplace_back("fourth");

Avoids the overhead of copying into the container.

Emplace works similarly for inserting into any position by iterator.

Resizing a Vector

Although vectors handle growth automatically, avoid reallocation by reserving enough capacity upfront:

vector<string> myStrings;
myStrings.reserve(100); // Avoid reallocating for 100 elements

The resize() method also sets capacity while letting you set the size:

myStrings.resize(100); // Size 100, with capacity for 100

Resizing with a smaller size truncates excess elements.

Keep capacity aligned with expected usage to maximize performance.

Accessing Vector Strings

Access elements just like a traditional C array:

string str = myStrings[0]; // Reads first string

Values can also be set with the indexing operator:

myStrings[1] = "set string"; 

Iteration supports direct access to the underlying string elements:

for (string str : myStrings) {
  // str has a copy of each string  
}

for (auto& str : myStrings) {
  // str is a reference to the actually vector elements 
}

Prefer indexed access when possible for optimal speed. Otherwise leverage C++11 range-based for loops for convenience.

Erasing Vector Elements

Erase elements by index position:

myStrings.erase(myStrings.begin() + 2); // Erase third element

Or provide an iterator range to remove multiple elements:

myStrings.erase(myStrings.begin() + 2, myStrings.begin() + 5);  

The erase methods shuffle down all elements after the erasure point.

To simply drop the final elements, use:

myStrings.resize(2); // Truncate length to 2 elements

Carefully check all iterator and index usage after erasing since positions will change.

Sorting and Comparing Strings

To alphabetize or sort strings:

sort(myStrings.begin(), myStrings.end()); 

By default, the < functional > sort uses string‘s built-in comparison operators to order lexicographically.

Supply a custom comparator function to override the ordering logic:

bool LengthCompare(const string &a, const string &b) {
  return a.size() < b.size(); 
}

sort(myStrings.begin(), myStrings.end(), LengthCompare); // Sort by length  

Custom predicates give you ultimate flexibility.

Using Custom String Classes

For special string behavior, build your own custom string class:

class CustomString {
private:
  string data;  
public:

  // Constructor 
  CustomString(const string& init) : data(init) { }  

  // Get underlying string
  string get() { return data; } 

};

Then use this class in vector declarations:

vector<CustomString> customStrings;

You now have complete control over strings while leveraging vector convenience methods.

Passing String Vectors to Functions

String vectors work great for passing arrays of text between functions:

void DisplayStrings(const vector<string>& strings) {
  for (auto str : strings) {
    cout << str << "\n"; 
  }
}

DisplayStrings(myStrings);

Pass by const reference allows access without copying the entire vector.

Return strings vectors directly back to callers:

vector<string> TransformStrings(vector<string> strings) {

  // Modify vector...

  return strings;
}

myStrings = TransformStrings(myStrings);

This avoids the overhead of copying into a return value.

String Vectors and Thread Safety

String classes like std::string handle their own internal synchronization. But the standard vector class itself is not thread-safe for concurrent modification by multiple threads.

Protect shared state during threaded access with a mutex:

mutex stringVectorMutex; 

void Thread1() {
  scoped_lock lock(stringVectorMutex);
  myStrings.push_back("a");
}

void Thread2() {
  scoped_lock lock(stringVectorMutex);  
  myStrings.erase(3); 
}

The mutex guarantees exclusive access when modifying elements.

Prefer thread-local copies instead where possible:

vector<string> localStrings = myStrings; // Make thread copy 

localStrings.insert(1, "b"); // Modify separately  

Consolidate back to main vector later by merging.

Joining a String Vector

To combine strings using a delimiter like CSV:

string JoinStringVector(const vector<string>& strings, string delim = ",") {

  string joined;

  for (const string& s : strings) {  
    joined += s + delim;
  }

  return joined.substr(0, joined.length() - 1); // Remove extra delim

}

string result = JoinStringVector(myStrings); // Comma separate 

Allow the caller to customize the delimiter character used between elements.

Streaming a String Vector

Easily format vectors for logging or output with stream operators:

ostream& operator<<(ostream& stream, const vector<string>& strings) {

  stream << "[";

  for (int i = 0; i < strings.size(); ++i) {
    stream << strings[i];
    if (i != strings.size() - 1) {
      stream << ", "; 
    }
  }

  stream << "]";

  return stream;
}

Usage:

vector<string> names {"Bob", "Tim"}; 

cout << names; // Prints [Bob, Tim]

Overloading << and >> enables clean integration with existing output streams.

Strings vs Alternate Vector Types

The standard library provides a few vector flavor options:

vector – Dynamic array, optimized for traversal and indexing

deque – Double-ended queue, fast prepends / appends like vector

list – Doubly linked list, efficient insertion / removal mid sequence

For string processing, vector is generally ideal because indexed access is frequently needed. Lists introduce caching issues since memory is not contiguous.

Deque can be useful where frequent queue-like operations predominate and indexed access is secondary.

If references to stored strings are stable, a vector strikes the best complexity balance. Be sure to reserve sufficient capacity during usage spikes to prevent reallocation.

Preferring String Views

To avoid copying long strings, consider storing std::string_view instead of std::string in vectors:

vector<string_view> lines; 

string_view line = LoadLine();
lines.push_back(line); 

String views only store a pointer and length, avoiding duplication while still providing a string interface.

But be cautious accessing underlying c-style strings, as std::string handles null termination.

Best Practices for Vector String Usage

Here are some key tips for working efficiently with C++ vectors storing strings:

• Specify capacity with reserve() before adding many elements
• Initialize vectors from the start instead of incrementally growing
• Use emplace/emplace_back to construct strings in-place
• Shrink vectors explicitly via resize if smaller
• Sort strings alphabetically with the default comparator
• Pass large vectors between functions using const reference
• Protect shared state across threads using a mutex
• Stream vectors using cout << myStrings for quick debugging

Carefully following best practices for incrementally developing string vectors will prevent performance pitfalls.

Key Takeaways

C++ vectors provide a dynamic, contiguous storage for strings needing fast indexed access. Their flexibility makes usage pervasive in all kinds of string processing tasks.

By understanding initialization options, insert vs erase characteristics, and thread safety considerations, you will gain mastery over this foundational technique.

There is far more that could be said, but this guide covers the key concepts critical for leveraging the expressiveness of the Standard Template Library for Robust string handling in vector containers.

Let me know if you have any other specific questions!