Question

注意其中有空格。

我可以使用哪种功能？

Answer 1

您可以使用

if (!strncmp("GET ", str, 4)
{ 
   ... 
} 
else if (!strncmp("POST ", str, 5)) 
{
   ...
} 
else
{
   ...
}

Answer 2

当您只需要区分几个字符串时， 不能使用strncmp()：

#include <stdio.h> #include <stdint.h> #include <string.h> static uint32_t method_hash(const char *key) { int len; uint32_t hash; int i; len = strlen(key); for (hash = 0, i = 0; i < len; i++) { hash += (unsigned int) key[i]; hash += (hash << 10); hash ^= (hash >> 6); } hash += (hash << 3); hash ^= (hash >> 11); hash += (hash << 15); return hash; } int main(int argc, char *argv[]) { if (argc < 2) { printf("Usage: %s <method>\n", argv[0]); return 0; } switch(method_hash(argv[1])) { case 802187597: printf("Its GET\n"); break; case 740659500: printf("Its POST\n"); break; default: printf("Its RUBBISH\n"); return 1; } return 0; }

请注意，哈希不是防冲突，但适合了解GET和POST之间的区别。我经常在词典中使用那个小宝石，当我想我有匹配时只调用strncmp()。

我发布这个答案告诉你，有很多方法可以处理字符串，希望你在继续学习C时避免看起来像这样的代码：

if (! strncmp(string, "FOO ", 4)) { do_this(); } else if (! strncmp(string, "BAR ", 4)) { do_that(); } else if (! strncmp(string, "FOOBAR ", 7)) { do_both(); /* ... madness ensues through 200 more lines and 100 more else if's ... */ } else { return 0; }

我的例子并不恰当。如果希望代码可移植，则需要在运行时确定哈希值，而不是仅插入已知值。这是读者的练习（提示，切换案例需要常量）。

Answer 3

将strncmp与参数string1，string2，n一起使用，其中string1和string2是要比较的字符串，n是字符数。如果字符串匹配，则strncmp返回0;如果字符串字典小于string2，则strncmp返回0;如果string2小于string1，则strncmp返回＆lt; 0例子：

#include <string.h>
...
strncmp(somestring, "GET ", 4) == 0
strncmp(somestring, "POST ", 5) == 0

Answer 4

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

typedef enum httpmethod
{
    HTTP_ERR,
    HTTP_GET,
    HTTP_POST,
    HTTP_METHOD_COUNT

} httpmethod;

const char* http_method_str[HTTP_METHOD_COUNT + 1] =
{
    "UNKNOWN",
    "GET ",
    "POST ",
    0
};


httpmethod str_get_http_method(const char* str)
{
    if (!str || strlen(str) < 4)
        return HTTP_ERR;

    const char* ptr[HTTP_METHOD_COUNT];
    int i;
    int failcount = 0;

    for (i = 1; i < HTTP_METHOD_COUNT; ++i)
        ptr[i] = http_method_str[i];

    while (*str != '\0' && failcount < HTTP_METHOD_COUNT - 1)
    {
        for (i = 1; i < HTTP_METHOD_COUNT; ++i)
        {
            if (ptr[i] && *str != *ptr[i]++)
            {
                ptr[i] = 0;
                ++failcount;
            }
        }
        str++;
    }

    for (i = 1; i < HTTP_METHOD_COUNT; ++i)
        if (ptr[i])
            return i;

    return HTTP_ERR;
}


int main(int argc, char** argv)
{
    const char* test[4] = { "GET ", "POST ", "GIT ", "PAST " };

    httpmethod result = HTTP_ERR;

    int i;

    for (i = 0; i < 4; ++i)
    {
        printf("checking str: %s\n", test[i]);
        result = str_get_http_method(test[i]);
        printf("result is type: %s\n", http_method_str[result]);
    }

    return 0;
}

如何检查字符串是否以c中的“GET”或“POST”开头？

4 个答案: