using strings as a pointer to its first character

Question

int main()  
{
    char name[]="avinash";   
    const char* nameano="a";   
    strtok(name,"n");   
    cout<<"the size of name is"<< sizeof(name);   
    cout<< name;
} 

strtok takes in arguments (char*, const char*); name is an array, and hence a pointer to its first element. But if we make a declaration like

string name="avinash";

and pass name as first argument to strtok, then the program doesn't work, but it should, because name, a string, is a pointer to its first character.

Also, if we write

const string n = "n";

and pass it as second argument it doesn't work; this was my first problem.

Now also the sizeof(name) output is 8, but it should be 4, as avinash has been tokenized. Why does this happen?

Answer 1

You are confusing several things.

strtok takes in arguments (char*, const char*)....name is an array and hence a pointer to its first element...

name is an array, and it's not a pointer to its first element. An array decays in a pointer to its first argument in several contexts, but in principle it's a completely different thing. You notice this e.g. when you apply the sizeof operator on a pointer and on an array: on an array you get the array size (i.e. the cumulative size of its elements), on a pointer you get the size of a pointer (which is fixed).

but if we made a declaration like string name="avinash" and passed name as argument then the prog doesnt work but it should because name of string is a pointer to its first character...

If you make a declaration like

string name="avinash";

you're are saying a completely different thing; string here is not a C-string (i.e. a char[]), but the C++ std::string type, which is a class that manages a dynamic string; those two things are completely different.

If you want to obtain a constant C-string (const char *) from a std::string you have to use it's c_str() method. Still, you can't use the pointer obtained in this way with strtok, since c_str() returns a pointer to a const C-string, i.e. it cannot be modified. Notice that strtok is not intended to work with C++ strings, since it's part of the legacy C library.

also if we write const string n = "n"; and pass it as second argument it doesnt work...this was my first problem...

这不适用于完全相同的动机，但在这种情况下，您可以简单地使用该c_str()方法，因为 的第二个参数strtok是 a 。const char *

现在 sizeof(name) 输出也是 8，但它应该是 4，因为 avinash 已被标记化..

sizeof返回其操作数的“静态”大小（即为其分配了多少内存），它对name. 要获得 C 字符串的长度，您必须使用该strlen函数；对于 C++，std::string只需使用它的size()方法。