The Development History of the C Language: Changes from C89 to C11

The C language is a widely used programming language that has undergone multiple standardizations since its inception in the early 1970s. This article will detail the development history of the C language, focusing on the significant changes between C89 and C11, and will provide code examples to help readers understand these changes.

1. C89 (ANSI C)

In 1989, the American National Standards Institute (ANSI) released the first official C language standard, known as ANSI C or C89. This version standardized the previous K&R C, allowing for better compatibility between different compilers.

Main Features:

• Function Prototypes: Introduced function prototypes, allowing the declaration of parameter types before calling functions.

  #include <stdio.h>
  void greet(const char *name);
  int main() {    greet("World");    return 0;}
  void greet(const char *name) {    printf("Hello, %s!\n", name);}

• Structures and Unions: Supported data definitions and operations for structures and unions.

• Preprocessor Directives: Enhanced support for macro definitions, conditional compilation, and other preprocessor directives.

2. C90

In 1990, the International Organization for Standardization (ISO) adopted ANSI C as an international standard, referred to as ISO C or C90. In fact, C90 did not have substantial differences from C89, only internationalizing it.

3. C99

In 1999, the second significant version—C99—was released. This version introduced several new features that made development easier for programmers.

New Features:

• Variable-Length Arrays: Allowed defining array sizes at runtime.

  #include <stdio.h>
  int main() {    int n;    printf("Enter the size of the array: ");    scanf("%d", &n);
      int arr[n]; // Variable-length array
      for (int i = 0; i < n; i++) {        arr[i] = i * i;        printf("%d ", arr[i]);    }
      return 0;}

• Inline Functions: Provided the inline keyword to suggest performance optimization by the compiler.

  inline int square(int x) {    return x * x;}
  // Using inline function

• New Data Types: Introduced new data types such as long long and boolean type bool.

  #include <stdbool.h>
  bool is_even(int num) {    return num % 2 == 0;}

4. C11

The third significant version released in 2011 is C11, which further expanded the language’s capabilities and improved multithreading support.

New Features:

• Multithreading Support: Introduced the <threads.h> library to support multithreaded programming.

  #include <stdio.h>
  #include <threads.h>
  int thread_function(void* arg) {    printf("Hello from thread!\n");    return (int)arg; // Return the parameter value passed to the thread}
  int main() {    thrd_t thread_id;    thrd_create(&thread_id, thread_function, (void*)42);
      thrd_join(thread_id, NULL); // Wait for the thread to finish
      return 0;}

• Static Assertions: Used _Static_assert() for compile-time checks to ensure certain conditions hold true.

  _Static_assert(sizeof(int) == sizeof(long), "Size of int must be equal to size of long.");

• Generic Selection Operator(_Generic): Allows selecting different code blocks to execute based on the type of an expression, enhancing code flexibility and readability.

  #define type_of(x) _Generic((x), 
      int: "int", 
      float: "float", 
      double: "double" 
  )
  const char* get_type(int a) {     return type_of(a); }
  // Calling get_type(5); will return "int"

Conclusion

From C89 in 1989 to C11 in 2011, the entire process demonstrates a trend of gradual evolution and continuous improvement. Each new version adds new features on top of the previous one to meet the growing demands of modern software development. By learning and utilizing these new features, we can not only enhance our coding skills but also better understand fundamental concepts in computer science. I hope this article helps you understand this historical process and the technical details behind it.