How do I add a new element to a string array in C?
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Is your array already full? Are you trying to increase the size of your array?David Weiser– David Weiser2011-01-31 16:48:56 +00:00Commented Jan 31, 2011 at 16:48
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Check this out, stackoverflow.com/questions/4694401/…Michael Smith– Michael Smith2011-01-31 16:51:04 +00:00Commented Jan 31, 2011 at 16:51
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So its an array of strings, or a string (an array of chars)? While similar, both cases have their own pitfalls.PeterK– PeterK2011-02-01 17:28:35 +00:00Commented Feb 1, 2011 at 17:28
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4 Answers
If it's a string, you'd just use strcat() (some docs). Just be wary that you can only extend as much as you've allowed memory for. You may have to realloc(), like another poster said.
Comments
A string in C is composed of an array of characters. In order for the string to be correctly printed using printf calls, it must be terminated by the NULL character (\0).
To add a new element ie. a character, to the end of a string, move to the NULL character & replace it with the new character, then put back the NULL after it. This assumes that sufficient space is already available for the new character.
char str[100];
char new_char = 'a';
int i = 0;
...
// adds new_char to existing string:
while(str[i] != '\0')
{
++i;
}
str[i++] = new_char;
str[i] = '\0';
2 Comments
try it out in your compiler: in this context,
str[i++] = new_char; is equivalent to str[i] = new_char; i++; If still in doubt refer to stackoverflow.com/q/4865599/191776If you want to extend your array, you need to reallocate memory for it. Check out realloc.
Comments
It depends on what you call an array.
if you have staticaly allocated a fixed length array, then you can just copy data in the i-th element.
char foo[25][25];
strcpy(foo[1], "hello world"); /* "puts" hello world in the 2nd cell of the array */
If you have used a dynamic array, you must first insure that there is still space, otherwize allocate memory, then put your item the same way.
5 Comments
Yasir Arsanukayev
@James: You can modify elements from
0 to 24, otherwise you write to a wrong area in memory, which may result in data loss and/or program crash. foo[1] is a pointer to the second array element, the second string.
bstpierre
Where are you getting your
strdup? It doesn't look like the standard version.
Aif
@bstpierre: you're right, code updated. @Yasir: thanks for explainations!
Georg Fritzsche
Your array declaration syntax wrong (should be
char foo[25][25]). Also you can't just assign a dynamically allocated string (a pointer) to an array. Try to compile your example...