Safely resizing a C-style string is a bit tricky because C-style strings are essentially arrays of characters, and arrays in C++ have a fixed size once they're created. However, we can implement a safe resizing operation by allocating a new buffer and copying the contents. Here's a step-by-step approach:
- Allocate a new buffer with the desired size.
- Copy the contents of the old buffer to the new one.
- Null-terminate the new buffer.
- Delete the old buffer (if it was dynamically allocated).
- Update the pointer to point to the new buffer.
Here's an example implementation:
#include <iostream>
#include <cstring>
#include <algorithm>
// Function to safely resize a C-style string
char* resizeString(
const char* oldStr, size_t newSize
) {
size_t oldSize = std::strlen(oldStr);
char* newStr = new char[newSize];
// Copy old string contents, ensuring we
// don't overflow
std::memcpy(
newStr, oldStr, std::min(oldSize, newSize - 1)
);
// Ensure null-termination
newStr[std::min(oldSize, newSize - 1)] = '\0';
return newStr;
}
int main() {
const char* original = "Hello, World!";
std::cout << "Original: " << original << '\n';
// Resize to a larger buffer
char* enlarged = resizeString(
original, 30); // Increase the buffer size
strncat_s(enlarged, 30, " How are you?",
30 - std::strlen(enlarged) - 1);
std::cout << "Enlarged: " << enlarged << '\n';
// Resize to a smaller buffer (truncation occurs)
char* shortened = resizeString(original, 9);
std::cout << "Shortened: " << shortened;
// Clean up
delete[] enlarged;
delete[] shortened;
}Original: Hello, World!
Enlarged: Hello, World! How are you?
Shortened: Hello, WThis approach ensures that we don't overflow our buffer, even when resizing to a smaller size. Note a few important points:
- We use
std::strncpy()instead ofstd::strcpy()to avoid buffer overflows. - We explicitly null-terminate the new string to ensure it's always valid.
- We're using dynamic allocation (
newanddelete[]), which means we need to manage memory manually.
To make this safer and more C++-like, we could use smart pointers:
#include <iostream>
#include <cstring>
#include <memory>
#include <algorithm>
std::unique_ptr<char[]> resizeString(
const char* oldStr, size_t newSize
) {
size_t oldSize{std::strlen(oldStr)};
auto newStr{std::make_unique<char[]>(newSize)};
std::copy(
oldStr,
oldStr + std::min(oldSize, newSize - 1),
newStr.get()
);
newStr[newSize - 1] = '\0';
return newStr;
}
void safeConcat(
std::unique_ptr<char[]>& dest,
const char* src,
size_t destSize
) {
size_t destLen = std::strlen(dest.get());
size_t srcLen = std::strlen(src);
if (destLen + srcLen >= destSize) {
srcLen = destSize - destLen - 1;
}
std::copy(
src, src + srcLen, dest.get() + destLen
);
dest[destLen + srcLen] = '\0';
}
int main() {
const char* original{"Hello, World!"};
std::cout << "Original: "
<< original << '\n';
auto enlarged{resizeString(original, 28)};
safeConcat(enlarged, " How are you?", 28);
std::cout << "Enlarged: "
<< enlarged.get() << '\n';
auto shortened{resizeString(original, 8)};
std::cout << "Shortened: "
<< shortened.get() << '\n';
}Original: Hello, World!
Enlarged: Hello, World! How are you?
Shortened: Hello,This version uses std::unique_ptr to manage the memory, eliminating the need for manual delete calls and reducing the risk of memory leaks.
Remember, while these methods work, they're not as efficient or safe as using std::string. Whenever possible, prefer std::string for string manipulation in C++.
Answers to questions are automatically generated and may not have been reviewed.
Working with C-Style Strings
A guide to working with and manipulating C-style strings, using the
