Test Case: c-instruct-134

### HTTP Response Code Parser Function
#### Overview
The following C function, `parse_http_response`, takes a string representing an HTTP response as input, extracts the response code, and checks if it falls within the 2xx range. If the response code is not 2xx, it increments an error counter and prints a warning message to the console. The function utilizes standard library functions and mutexes to ensure thread-safety.

#### Code
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>

// Error counter
int error_count = 0;

// Mutex for thread-safety
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

/**
 * Parse an HTTP response and check if the response code is 2xx.
 *
 * @param response The HTTP response string.
 *
 * @return The HTTP response code.
 */
int parse_http_response(const char* response) {
    // Find the response code in the HTTP response string
    const char* code_start = strstr(response, "HTTP/");
    if (code_start == NULL) {
        // If the response code is not found, return -1
        return -1;
    }

    // Extract the response code
    code_start += 8; // Skip "HTTP/1.1 "
    char code_str[4];
    strncpy(code_str, code_start, 3);
    code_str[3] = '\0';

    // Convert the response code to an integer
    int response_code = atoi(code_str);

    // Check if the response code is 2xx
    if (response_code < 200 || response_code >= 300) {
        // Increment the error counter and print a warning message
        pthread_mutex_lock(&mutex);
        error_count++;
        printf("Warning: Non-2xx response code %d\n", response_code);
        pthread_mutex_unlock(&mutex);
    }

    return response_code;
}

int main() {
    const char* response = "HTTP/1.1 200 OK";
    int response_code = parse_http_response(response);
    printf("Response code: %d\n", response_code);

    return 0;
}
```

#### Explanation
1. The `parse_http_response` function takes a string representing an HTTP response as input.
2. It finds the response code in the HTTP response string by searching for the "HTTP/" substring.
3. The response code is extracted and converted to an integer using `atoi`.
4. The function checks if the response code is 2xx. If not, it increments the error counter and prints a warning message to the console.
5. The `main` function demonstrates the usage of `parse_http_response` with an example HTTP response string.

#### Compilation and Execution
To compile and execute the code, save it to a file named `http_response_parser.c` and run the following commands:
```bash
gcc -o http_response_parser http_response_parser.c -lpthread
./http_response_parser
```
This will compile the code and execute the `main` function, which will print the response code and a warning message if the response code is not 2xx.

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>

// Structure to hold HTTP response data
typedef struct {
    char* response;
    int length;
    int error_count;
    pthread_mutex_t mutex;
} http_response_t;

// Function to parse HTTP response and check status code
int parse_http_response(http_response_t* response) {
    // Initialize mutex if not already initialized
    if (pthread_mutex_init(&response->mutex, NULL)!= 0) {
        printf("Mutex initialization failed\n");
        return -1;
    }

    // Lock mutex for thread safety
    pthread_mutex_lock(&response->mutex);

    // Find the start of the status line
    char* status_line = strstr(response->response, "HTTP/");

    // If status line not found, return error
    if (status_line == NULL) {
        pthread_mutex_unlock(&response->mutex);
        return -1;
    }

    // Extract the status code
    char* status_code_str = strstr(status_line, " ");
    if (status_code_str == NULL) {
        pthread_mutex_unlock(&response->mutex);
        return -1;
    }
    status_code_str++;

    // Convert status code string to integer
    int status_code = atoi(status_code_str);

    // Check if status code is 2xx
    if (status_code < 200 || status_code >= 300) {
        // Increment error count
        response->error_count++;

        // Print warning message
        printf("Warning: Non-2xx status code %d received\n", status_code);
    }

    // Unlock mutex
    pthread_mutex_unlock(&response->mutex);

    // Return status code
    return status_code;
}
```