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我试图在 C 中实现哈希表来存储英文单词。所以我在互联网上搜索了一些最好的非加密哈希函数。其中一些是Murmurhash、Seahash、xxHash，但它们似乎都很难实现。所以我搜索了一些更简单的，然后我发现了DJB2, sdbm, lost loss。在实施 sdbm 我得到了这个

try.c:12:18: error: using the result of an assignment as a condition without 
parentheses [-Werror,-Wparentheses]
    while (c = *str++)
           ~~^~~~~~~~
try.c:12:18: note: place parentheses around the assignment to silence this 
warning
    while (c = *str++)
             ^
           (         )
try.c:12:18: note: use '==' to turn this assignment into an equality 
comparison
    while (c = *str++)
             ^
             ==
try.c:26:31: error: passing 'char *' to parameter of type 'unsigned char *' 
converts between pointers to integer types with
  different sign [-Werror,-Wpointer-sign]
unsigned long hash = sdbm(argv[1]);
                          ^~~~~~~
2 errors generated.

我的代码是

#include <cs50.h> 
#include <string.h>
#include <stdio.h>

static unsigned long
sdbm(str)
unsigned char *str;
{
    unsigned long hash = 0;
    int c;

    while (c = *str++)
        hash = c + (hash << 6) + (hash << 16) - hash;

    return hash;
}

int main(int argc,char *argv[])
{
if(argc!=2)
{
    printf("Enter the second command line argument\n");
    return 1;
}

unsigned long hash = sdbm(argv[1]);
printf("The returned hashcode is %lu\n", hash);
}

如果你也可以帮助我处理 Murmurhash、Seahash 或 xxHash，请这样做。

4

1 回答 1

1

哎呀！这个带有简单参数列表的函数定义是一个过时的特性：

static unsigned long
sdbm(str)
unsigned char *str;
{

标准方法是（至少自 80 年代后期以来）是使用原型定义：

static unsigned long
sdbm(unsigned char *str)
{

现在对于错误：

while ((c = *str++))
    ...

括号告诉编译器您测试分配的结果值。

unsigned long hash = sdbm((unsigned char *) argv[1]);

只是强制转换为预期的指针类型。

于 2018-02-02T11:39:03.550 回答