Question

I have a const char* variable which takes values from a function that I have wrote.

When I write this variable to a file many times it writes nothing. So it must be empty or filled in with space.The strange thing is that in the txt file that I write it changes line every time, when it has value or not.Why is that?Does it mean that the returned value from the function has a \n?

how can I check if a value of a const char * is empty or in general how can I check character by character the value in char*?

Answer 1

Since C/C++ pointers can be interpreted as arrays of values the pointers point to, the two ways of checking values of a char* is by applying an indexing operator or by using pointer arithmetics. You can do this:

const char *p = myFunctionReturningConstChar();
for (int i = 0 ; p[i] ; i++) {
    if (p[i] == '\n') printf("New line\n");
}

or this:

const char *p = myFunctionReturningConstChar();
while (*p) {
    if (*p == '\n') printf("New line\n");
    p++;
}

In addition, C++ library provides multiple functions for working with C strings. You may find strlen helpful to check if your pointer points to an empty string.