Detailed explanation of C language array and pointer pen test questions (difference between integer array, character array, sizeof, strlen)

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foreword

This article mainly introduces the written test questions related to C language pointers and arrays.

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1. Array-related written test questions

(1) Integer array

Let's look at the first group of questions first:

#include <stdio.h>
int main()
{
    
    
    int a[] = {
    
     1,2,3,4 };
    printf("%d\n", sizeof(a));
    printf("%d\n", sizeof(a + 0));
    printf("%d\n", sizeof(*a));
    printf("%d\n", sizeof(a + 1));
    printf("%d\n", sizeof(a[1]));
    return 0;
}

sizeof(): Find the length of the array (it returns the number of bytes of memory occupied by an object or type)

The diagram is as follows:

Topic 2:

#include <stdio.h>
int main()
{
    
    
    int a[] = {
    
     1,2,3,4 };
    printf("%p\n", &a);
    printf("%p\n", &a + 1);
    printf("%p\n", &a[0]);
    printf("%p\n", &a[0] + 1);
    return 0;
}

The diagram is as follows:

(2) Character array

Let's first understand the difference between sizeof and strlen .
sizeof: It is a unary operator in C language, and its operands can be data types, functions, variables, etc. For example, calculate the storage space of int type data: sizeof(int)

strlen: Calculate the length of a string. Provided by the standard library of the C language.
Note : When strlen calculates the length of the string, the '\0' character is used as the end mark.

Consider this example:

#include <stdio.h>
#include<string.h>
int main()
{
    
    
    char a1[] = {
    
     'h','e','l','l','o' };
    char a2[] = "hello";
    printf("%d\n", sizeof(a1));
    printf("%d\n", sizeof(a2));
    printf("%d\n", strlen(a1));
    printf("%d\n", strlen(a2));
    return 0;
}

The diagram is as follows:

topic:

#include <stdio.h>
#include<string.h>
int main()
{
    
    
    char arr[] = {
    
     'h','e','l','l','o' };
    printf("%d\n", sizeof(arr));
    printf("%d\n", sizeof(*arr));
    printf("%d\n", sizeof(arr[1]));
    printf("%d\n", sizeof(&arr));
    printf("%d\n", sizeof(&arr + 1));
    printf("%d\n", sizeof(&arr[0] + 1));
    return 0;
}

The result is as follows:

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Two, the pointer

(1) Topic 1:

#include <stdio.h>
int main()
{
    
    
    int a[5] = {
    
     1, 2, 3, 4, 5 };
    int *ptr = (int *)(&a + 1);
    printf( "%d,%d", *(a + 1), *(ptr - 1));
    return 0;
}

Result analysis:

(2) Topic 2:

int main()
{
    
    
    int a[4] = {
    
     1, 2, 3, 4 };
    int *ptr1 = (int *)(&a + 1);
    int *ptr2 = (int *)((int)a + 1);
    printf( "%x,%x", ptr1[-1], *ptr2);  //%x以16进制打印
    return 0;
}

Result analysis:

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Summarize

That's all for this article.