[Term-Entry] C++ Strings c_str()

content/cpp/concepts/strings/terms/c-str/c-str.md

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+---
+Title: '.c_str()'
+Description: 'Returns a pointer to a null-terminated character array that represents the contents of the string.'
+Subjects:
+  - 'Computer Science'
+  - 'Game Development'
+Tags:
+  - 'Arrays'
+  - 'Methods'
+  - 'Strings'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+In C, the **`.c_str()`** method returns a [pointer](https://www.codecademy.com/resources/docs/cpp/pointers) to a null-terminated [array](https://www.codecademy.com/resources/docs/cpp/arrays) of characters, equivalent to the contents of the string on which it is called.
+
+The `c_str()` method is commonly used when a C-style string is needed, such as when passing a `std::string` to functions that expect a `const char*`. It's especially useful for interoperability with legacy C libraries or APIs like [`printf()`](https://www.codecademy.com/resources/docs/c/basic-output/printf), `fopen()`, or other system-level functions.
+
+> **Note:** The `.c_str()` method runs in constant time O(1), as it returns a pointer to the internal character array of the std::string.
+
+## Syntax
+
+```pseudo
+string.c_str()
+```
+
+**Parameters:**
+
+The `.c_str()` method does not take any parameters.
+
+**Return value:**
+
+Returns a `const char*`, which is a pointer to a null-terminated character array representing the contents of the string.
+
+## Example
+
+This example shows the size of a `std::string` object and a pointer returned by `.c_str()`, along with the actual string length using [`length()`](https://www.codecademy.com/resources/docs/cpp/strings/length) and [`strlen()`](https://www.codecademy.com/resources/docs/c/strings/strlen):
+
+```cpp
+#include <string>
+#include <iostream>
+#include <cstring> // for strlen
+
+int main() {
+  std::string str = "Foobar";
+  const char* arr = str.c_str();
+
+  std::cout << "Size of 'arr' (pointer): " << sizeof(arr) << " bytes" << std::endl;
+  std::cout << "Size of 'str' (std::string object): " << sizeof(str) << " bytes" << std::endl;
+
+  std::cout << "Length of string using str.length(): " << str.length() << std::endl;
+  std::cout << "Length of string using strlen(arr): " << strlen(arr) << std::endl;
+
+  return 0;
+}
+```
+
+The output of this code is:
+
+```shell
+Size of 'arr' (pointer): 8 bytes
+Size of 'str' (std::string object): 32 bytes
+Length of string using str.length(): 6
+Length of string using strlen(arr): 6
+```
+
+> **Note:** [`sizeof`](https://www.codecademy.com/resources/docs/c/operators/sizeof) gives the size of the variable's type, not the number of characters.
+
+## Codebyte Example
+
+In this codebyte example, we have a function `printPointerCharArrToStdOut` that expects a pointer to a character array. The `.c_str()` method is used to convert a `std::string` to a C-style string, allowing it to be passed to the function. The function then outputs each character of the array individually:
+
+```codebyte/cpp
+#include <string>
+#include <iostream>
+#include <cstring> // for strlen
+
+void printPointerCharArrToStdOut(const char* arr) {
+  const int size = strlen(arr);
+  for (int i = 0; i < size; ++i) {
+    std::cout << *(arr + i) << std::endl;
+  }
+}
+
+int main() {
+  std::string str = "StrArray";
+  const char* cStr = str.c_str();
+  printPointerCharArrToStdOut(cStr);
+  return 0;
+}
+```