使用const替代变量声明的空指针

Question

我有个问题，我找不出来。我写了这个代码洗牌数组的元素：

#include <stdio.h> 
#include <stdlib.h> 
#include <time.h> 

const char *array[]={"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"}; 

int main(int argc, char **argv) 
{ 
int i, tmp, randomize, size; 

size = sizeof(array)/sizeof(*array); 

srand(time(NULL)); 

for(i=size;i>0;i--){ 
    randomize=0+(rand()%size); 
    tmp=(int)array[i]; 
    array[i]=array[randomize]; 
    array[randomize]=(char*)tmp; 
} 

for(i=0;i<size;i++) 
    printf("%s", array[i]); 
    return 0; 
} 

当我运行程序，这是iutput：

azlngiwexbv(null)uscphqjyrodmtk 

我不明白为什么指针有时是零，我不明白为什么，以这种方式更改源代码：

#include <stdio.h> 
#include <stdlib.h> 
#include <time.h> 

int main(int argc, char **argv) 
{ 
char *array[]={"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"}; 
int i, tmp, randomize, size; 

size = sizeof(array)/sizeof(*array); 

srand(time(NULL)); 

for(i=size;i>0;i--){ 
    randomize=0+(rand()%size); 
    tmp=(int)array[i]; 
    array[i]=array[randomize]; 
    array[randomize]=(char*)tmp; 
} 

for(i=0;i<size;i++) 
    printf("%s", array[i]);  
return 0; 
} 

一切工作正常。 谢谢。

Answer 1

从size-1开始循环，您指出array[size]（第一次循环迭代）中的数组。

for (i=size-1; i>=0; i--) 

Answer 2

您应该尽可能避免铸造，而且很少有必要这样做。

除非您计划使用argc和argv[]，请使用更简单的表格main()：int main(void)。这将删除一些编译器警告，并且您应该启用这些警告;删除全部由您的编译器发出的警告。

你施放一个指针char到int将其存储在tmp，然后你施放tmp回到(char *)。只需声明tmp作为指向char开始。第一个循环从size倒数到0;这已经超出了数组范围，但为什么不使用传统的循环结构：for (i = 0; i < size; i++)？另外，你应该考虑使用size_t作为数组索引;它是一个无符号整数类型，保证能够保存任何数组索引，并且也是由sizeof运算符返回的类型。

此外，在您的第一个版本中，您已将array声明为指向const char的指针数组。您可以执行此操作，但需要临时存储变量tmp与const类型限定符一致。

以上是您的代码与上述更改。没有演员，编译没有警告，它的工作。

#include <stdio.h> 
#include <stdlib.h> 
#include <time.h> 

int main(void) 
{ 
    const char *array[] = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"}; 

    const char *tmp; 
    size_t i, size; 
    int randomize; 

    size = sizeof(array)/sizeof(*array); 

    srand(time(NULL)); 

    for(i = 0; i < size; i++){ 
     randomize = (rand() % size); 
     tmp = array[i]; 
     array[i] = array[randomize]; 
     array[randomize] = tmp; 
    } 

    for(i = 0; i < size; i++) 
     printf("%s", array[i]); 
    putchar('\n'); 

    return 0; 
}