指向结构指针内字符串中的字符

Question

Normally in C you can point to a specific char of a string to obtain a substring. Example:

char string[10];
strcpy(string, "foo bar");
char *substring = &string[4];

// string = "foo bar"
// substring = "bar"

But what would be the syntax when you are dealing with struct pointers? I thought it would be something like this but it returns garbage data:

struct line
{
    char string[10];
    char substring[10];
};

void some_function(struct line *txt)
{
    *(txt->substring) = &(txt->string[4]);
}

int main()
{
    struct line text;
    strcpy(text.string, "foo bar");

    some_function(&text);
    printf("\n-%s-\n", text.string);
    printf("\n-%s-", text.substring); // returns garbage data

    return 0;
}

Answer 1

It seems you mean

void some_function(struct line *txt)
{
    strcpy( txt->substring, txt->string + 4 );
}

The data member substring does not have a pointer type. It is an array. So you may not assign a pointer to an array. You can copy elements of one array to another array.

As for this expression statement

*(txt->substring) = &(txt->string[4]);

then the left operand has the type char while the right operand has the type char * . So this assignment in any case does not make sense.

If the structure would be defined like

struct line
{
    char string[10];
    char *substring;
};

then within the function you could write

void some_function(struct line *txt)
{
    txt->substring = txt->string + 4;
}