How can I join a char to a constant char*?

I have a function that joins two constant char* and returns the result. What I want to do though is join a char 开发者_Python百科to a constant char* eg

char *command = "nest";
char *halloween =  join("hallowee", command[0]);   //this gives an error

char *join(const char* s1,  const char* s2)
{
    char* result = malloc(strlen(s1) + strlen(s2) + 1);

    if (result)
    {
            strcpy(result, s1);
            strcat(result, s2);
    }

    return result;
}

The function you wrote requires two C-strings (i.e. two const char * variables). Here, your second argument is command[0] which is not a pointer (const char *) but a simple 'n' character (const char). The function, however, believes that the value you passed is a pointer and tries to look for the string in memory adress given by the ASCII value of the letter 'n', which causes the trouble.

EDIT: To make it work, you would have to change the join function:

char *join(const char* s1,  const char c)
{
    int len = strlen(s1);
    char* result = malloc(len + 2);

    if (result)
    {
            strcpy(result, s1);
            result[len] = c;         //add the extra character
            result[len+1] = '\0';    //terminate the string
    }

    return result;
}

If you wish to join a single character, you will have to write a separate function that takes the quantity of characters from s2 to append.

The best is to create a new function that allows adding a single char to a string. But if you would like to use the join() function as it is for some reason, you can also proceed as follows:

char *command = "nest";
char *buffer  = " "; // one space and an implicit trailing '\0'
char *halloween;

*buffer = command[0];
halloween = join("hallowee", buffer);