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© 2025 long

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C-Base

Posted at 2020-09-03 笔记 C 

计算数组的大小

sizeof(数组名) 获得这个数组占用内存的总长度。二维数组是全部元素占用的总长度。

长度 = sizeof(数组名) / sizeof(数组类型)

元素个数 = 总的占用字节大小 / 每个元素占用的字节大小

64位指针占用8字节，8×8=64，内存寻址。

计算一维数组长度

例子1：

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char *sc4[] ={"hello","world","Welcome","C"};
   printf("arr total byte = %ld\n",sizeof(sc4));
   printf("arr single element byte = %ld\n",sizeof(sc4[0]));
   printf("arr length = %ld\n",sizeof(sc4)/sizeof(sc4[0]));
   printf("arr length = %ld\n",sizeof(sc4)/sizeof(*sc4));

输出：

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arr total byte = 32
arr single element byte = 8
arr length = 4
arr length = 4
arr total byte = 32

例子2：

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int n[8] = {1,2,3,4,5};
  printf("arr total byte = %ld\n",sizeof(n));
  printf("arr single element byte = %ld\n",sizeof(n[0]));
  printf("arr length = %ld\n",sizeof(n)/sizeof(n[0]));
  printf("arr length = %ld\n",sizeof(n)/sizeof(*n));

输出：

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arr total byte = 32
arr single element byte = 4
arr length = 8
arr length = 8

计算二维数组长度

例子1：

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char* arr2[2][3];
   printf("total byte = %ld\n",sizeof(arr2));
   printf("row byte = %ld\n",sizeof(arr2[0]));
   printf("column byte = %ld\n",sizeof(arr2[0][0]));
   printf("rows = %ld\n",sizeof(arr2) / sizeof(arr2[0]));
   printf("rows = %ld\n",sizeof(arr2) / sizeof(*arr2));
   printf("columns = %ld\n",sizeof(arr2[0])/sizeof(arr2[0][0]));
   printf("columns = %ld\n",sizeof(*arr2)/sizeof(**arr2));

输出：

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total byte = 48
row byte = 24
column byte = 8
rows = 2
rows = 2
columns = 3
columns = 3

例子2：

定义一个结构体：

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typedef struct People_s {
    char *name;
    int age;
}People;
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People arr3[3][9];
  printf("total byte = %ld\n",sizeof(arr3));
  printf("row byte = %ld\n",sizeof(arr3[0]));
  printf("column byte = %ld\n",sizeof(arr3[0][0]));
  printf("rows = %ld\n",sizeof(arr3) / sizeof(arr3[0]));
  printf("rows = %ld\n",sizeof(arr3) / sizeof(*arr3));
  printf("columns = %ld\n",sizeof(arr3[0])/sizeof(arr3[0][0]));
  printf("columns = %ld\n",sizeof(*arr3)/sizeof(**arr3));

输出：

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total byte = 432
row byte = 144
column byte = 16
rows = 3
rows = 3
columns = 9
columns = 9

valgrind 检查内存泄漏

valgrind --leak-check=full --track-origin=yes ./test

C的字符串数组

第一种情况,每一个都是指针

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char **arr = NULL;
// 10 个字符串
arr = calloc(10, sizeof(char *));
arr[0] = calloc(1, 100);
strcpy(arr[0], "Hello");
arr[1] = calloc(1, 100);
strcpy(arr[1], "World");

第二种情况,确定字符串的个数,但每个字符串长度不确定

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char *print2[10];
for (int i = 0; i < 10; ++i) {
    print2[i] = calloc(1, i + 2);
    sprintf(print2[i], "%d", i);
}
for (int i = 0; i < 10; ++i) {
    printf("%s\n", print2[i]);
    free(print2[i]);
}

第三种情况,字符串的个数和字符串的长度已经确定

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char print[2][10] = {"Hello", "World"};
for (int i = 0; i < 2; ++i) {
    printf("%s\n", print[i]);
}

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© 2025 long

Theme Typography by Makito

Proudly published with Hexo