优化了命名

C06-指针/const.c

@@ -0,0 +1,91 @@
+/**
+ *   const int a;
+ *   int const a;
+ *
+ *   常量指针
+ *   const int *p;
+ *   int const *p;
+ *
+ *   指针常量
+ *   int *const p;
+ *
+ *   const int *const p;
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define PI 3.14
+
+int main()
+{
+    int i = 1;
+    int j = 100;
+
+    const int *const p = &i;
+
+    //(F) p = &j;
+
+    //(F) *p = 10;
+
+
+#if 0
+    int *const p = &i;
+
+    //(T) *p = 10;
+
+    //(F) p = &j;
+    // [main][~/workspace/Linux-C-Notes/Chapter6]$ make const
+    // cc     const.c   -o const
+    // const.c: In function ‘main’:
+    // const.c:29:7: error: assignment of read-only variable ‘p’
+    //    29 |     p = &j;
+    //       |       ^
+    // make: *** [<builtin>: const] Error 1
+
+    printf("i = %d\n", *p);
+
+#endif
+
+#if 0
+    int i = 1;
+    int j = 2;
+
+    // 常量指针
+    const int *p = &i;
+
+    //(T) i = 2;
+    // 直接用i改还是可以改成功的
+
+    //(F) *p = 2;
+
+    //(T) p = &j;
+
+    printf("i = %d\n", i);
+
+#endif
+
+
+#if 0
+    const float pi = 3.14;
+    // const 将变量常量化，相比于宏，多了检查语法
+
+    //(F) pi = 3.14159;
+
+    // float *p = &pi;
+    const float *p = &pi;
+
+    // *p = 3.14159;
+    // [main][~/workspace/Linux-C-Notes/Chapter6]$ make const
+    // cc     const.c   -o const
+    // const.c: In function ‘main’:
+    // const.c:28:16: warning: initialization discards ‘const’ qualifier from
+    // pointer target type [-Wdiscarded-qualifiers]
+    //    28 |     float *p = &pi;
+    //       |
+
+#endif
+
+    exit(0);
+}