Thread: How do you find the amount of space in a char array?

Please help.

You can use sizeof for a char array. If all you have is a pointer then there is no way.
Kurt

Well, this doesn't pop up my error message when I wrote this code though with sizeof :

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int Concatenate(char * Destination, char * StringToConcatenate);

int main()
{
    int Valid = 1;

    char String1[10] = {'T','h','e',' ','b','o','y','s',' '};
    char String2[7] = {'a', 'r', 'e', '.','.','.'};

    Valid = Concatenate(String1, String2);

    if (!Valid) printf("\n %s \n", String1); else printf("\n \a Not valid function parameters! \n \n");

    Valid = Concatenate(String1, String2);

    if (!Valid) printf("\n %s \n", String1); else printf("\n \a Not valid function parameters! \n \n");

    return 0;
}

int Concatenate(char * Destination, char * StringToConcatenate)
{
/* Sets charcount equal to the number of characters before the null terminator */
int charcount = 0;
char * Cptr;

Cptr = Destination;

while ( *Cptr != '\0') { charcount++; Cptr++; }

/* ------------------------------------------------------ */

/* Saves the data from the loop in a variable, and resets the pointer to the next array */

int String1CharacterAmount = charcount;
charcount = 0;
Cptr = StringToConcatenate;

/* ------------------------------------------------------ */

/* Same as the first segment of code in this function, except it counts the 2nd array */

while ( *Cptr != '\0') { charcount++; Cptr++; }

int String2CharacterAmount = charcount;
charcount = 0;

/* ------------------------------------------------------ */

if ((sizeof(Destination) / sizeof(char)) > (((sizeof(Destination) / sizeof(char)) - String1CharacterAmount) + ((sizeof(StringToConcatenate) / sizeof(char)) - String2CharacterAmount))) /* Makes sure there is enough space in the first array for the second */
{
    /* Returns 1 if not enough space */
    return 1;
} else
{
    /* This function returns 0 after sucessful completion, and this function also
    removes the null character and adds it back after concatenation */

    int c = 0;
    Cptr = Destination;

    if (*(Cptr+(String1CharacterAmount + 1)) == '\0') { *(Cptr+(String1CharacterAmount + 1)) = ' '; }

    for (; c < String2CharacterAmount; c++)
    {
        *(Destination + (String1CharacterAmount + c)) = *(StringToConcatenate + c);
    }

    *(Destination + ((String1CharacterAmount) + 1 + (String2CharacterAmount))) = '\0';

    return 0;
}

/* ------------------------------------------------------ */
}

All you have in Concatenate() is a pointers so sizeof won't help. You have to pass the sizes as well.
Kurt

I know it isn't large enough, I was trying to make it pop up an error message...

Thanks for all you help guys! This is the program I came up with

at the end.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int Concatenate(char * Destination, char * StringToConcatenate, size_t DestinationSize, size_t StringToConcatenateSize);

int main()
{
    int Valid = 1;

    char String1[24] = {'T','h','e',' ','b','o','y','s',' ','\0'};
    char String2[7] = {'a', 'r', 'e', '.','.','.','\0'};

    size_t SizeOfDestination;
    size_t SizeOfStringToConcatenate;

    SizeOfDestination = sizeof(String1);
    SizeOfStringToConcatenate = sizeof(String2);

    Valid = Concatenate(String1, String2, SizeOfDestination, SizeOfStringToConcatenate);

    if (!Valid) printf("\n %s \n", String1); else printf("\n \a Not enough array space! \n \n");

    Valid = Concatenate(String1, String2, SizeOfDestination, SizeOfStringToConcatenate);

    if (!Valid) printf("\n %s \n", String1); else printf("\n \a Not enough array space! \n \n");

    return 0;
}

int Concatenate(char * Destination, char * StringToConcatenate, size_t DestinationSize, size_t StringToConcatenateSize)
{

/* Sets charcount equal to the number of characters before the null terminator */

    int charcount = 0;
    char * Cptr;

    Cptr = Destination;

    while ( *Cptr != '\0') { charcount++; Cptr++; }

/* ------------------------------------------------------ */

/* Saves the data from the loop in a variable, and resets the pointer to the next array */

    int String1CharacterAmount = charcount;
    charcount = 0;
    Cptr = StringToConcatenate;

/* ------------------------------------------------------ */

/* Same as the first segment of code in this function, except it counts the 2nd array */

    while ( *Cptr != '\0') { charcount++; Cptr++; }

    int String2CharacterAmount = charcount;
    charcount = 0;

/* ------------------------------------------------------ */

    if (DestinationSize < ((DestinationSize - (DestinationSize - (String1CharacterAmount + 1))) + (StringToConcatenateSize - (StringToConcatenateSize - (String2CharacterAmount + 1))))) /* Makes sure there is enough space in the first array for the second */
    {
        /* Returns 1 if not enough space */
        return 1;
    } else
    {
        /* This function returns 0 after sucessful completion, and this function also
        removes the null character and adds it back after concatenation */

        int c = 0;
        Cptr = Destination;

        if (*(Cptr+(String1CharacterAmount + 1)) == '\0') { *(Cptr+(String1CharacterAmount + 1)) = ' '; }

        for (; c < String2CharacterAmount; c++)
    {
        *(Destination + (String1CharacterAmount + c)) = *(StringToConcatenate + c);
    }

    *(Destination + ((String1CharacterAmount) + 1 + (String2CharacterAmount))) = '\0';

    return 0;
}

/* ------------------------------------------------------ */
}

This program now works and displays an error message if the first array is too small.