c - 如何从函数返回字符数组？然后在另一个函数中使用返回的字符？

Question

    char * read_command()
{
        char command[25];

        char *input =  malloc(sizeof(char) * 25);
        printf("myRolodex Command: ");
        scanf("%c", &command);
        strcpy(input, command);
        return input;
}

void evaluate_command(char command[250])
{
        if (strcmp(command == 'I')==0)
        {
        printf("\nenterned i");
        }
}

int main()
{
evaluate_command(read_command))
return 0;
}

我尝试这样做，但编译时得到:

rolodex.c: In function ‘read_command’:
rolodex.c:25: warning: format ‘%c’ expects type ‘char *’, but argument 2 has type ‘char (*)[25]’
rolodex.c: In function ‘evaluate_command’:
rolodex.c:32: warning: comparison between pointer and integer
rolodex.c:32: warning: passing argument 1 of ‘strcmp’ makes pointer from integer without a cast
/usr/include/string.h:143: note: expected ‘const char *’ but argument is of type ‘int’
rolodex.c:32: error: too few arguments to function ‘strcmp’
rolodex.c: In function ‘main’:
rolodex.c:43: warning: passing argument 1 of ‘evaluate_command’ from incompatible pointer type
rolodex.c:30: note: expected ‘char *’ but argument is of type ‘char * (*)()’
rolodex.c:43: error: expected ‘;’ before ‘)’ token
rolodex.c:43: error: expected statement before ‘)’ token

我应该让“read_command可以打印提示，然后从用户那里读取一个字符。它可能想在返回之前确保该命令是有效的命令。

evaluate_command 可以接受一个命令字符并决定它是哪个命令，然后执行适当的操作。”

Answer 1

编译器错误的解释。不过，您的代码还存在其他问题

 char * read_command()
{
        char command[25];

        char *input =  malloc(sizeof(char) * 25);
        printf("myRolodex Command: ");
       scanf("%c", &command);

rolodex.c:25: warning: format ‘%c’ expects type ‘char ’, but argument 2 has type ‘char ()[25]’

所以这表明第二个参数的类型错误。您想将该字符放入 command 的第一个元素中。为此，您需要传递一个指向第一个字符的指针。您可以通过传递该字符的地址 -&command[0] 来完成此操作，尽管这与 command 相同。

        strcpy(input, command);
        return input;
}

void evaluate_command(char command[250])
{
    if (strcmp(command == 'I')==0)

rolodex.c:32: warning: comparison between pointer and integer

这一行有两个比较。 ==0 与 strcmp 的返回值进行比较，返回一个整数。所以不可能是那个人。

对于另一个，我们将指向字符的指针(命令)与字 rune 字(对于 C 来说只是一个整数)进行比较。所以这是错误的。

rolodex.c:32: warning: passing argument 1 of ‘strcmp’ makes pointer from integer

比较的结果是(在 C 语言中)一个整数。但您需要将字符串传递给strcmp。

rolodex.c:32: error: too few arguments to function ‘strcmp’

此外，strcmp 采用两个参数，那么这里发生了什么？您的意思大概是 strcmp(command, "I") 。

        {
        printf("\nenterned i");
        }
}

int main()
{
    evaluate_command(read_command))

rolodex.c:43: warning: passing argument 1 of ‘evaluate_command’ from incompatible pointer type rolodex.c:30: note: expected ‘char *’ but argument is of type ‘char * (*)()’ rolodex.c:43: error: expected ‘;’ before ‘)’ token rolodex.c:43: error: expected statement before ‘)’ token

readcommand 是一个函数。您必须调用它(使用readcommand())

      return 0;
   }