Converting int to string in C

Before I continue, I must warn you that itoa is NOT an ANSI function — it's not a standard C function. You should use sprintf to convert an int into a string.

itoa takes three arguments.

• The first one is the integer to be converted.
• The second is a pointer to an array of characters - this is where the string is going to be stored. The program may crash if you pass in a char * variable, so you should pass in a normal sized char array and it will work fine.
• The last one is NOT the size of the array, but it's the BASE of your number - base 10 is the one you're most likely to use.

The function returns a pointer to its second argument — where it has stored the converted string.

itoa is a very useful function, which is supported by some compilers - it's a shame it isn't support by all, unlike atoi.

If you still want to use itoa, here is how should you use it. Otherwise, you have another option using sprintf (as long as you want base 8, 10 or 16 output):

char str[5];
printf("15 in binary is %s\n",  itoa(15, str, 2));

Use snprintf, it is more portable than itoa.

itoa is not part of standard C, nor is it part of standard C++; but, a lot of compilers and associated libraries support it.

Example of sprintf

char* buffer = ... allocate a buffer ...
int value = 4564;
sprintf(buffer, "%d", value);

Example of snprintf

char buffer[10];
int value = 234452;
snprintf(buffer, 10, "%d", value);

Both functions are similar to fprintf, but output is written into an array rather than to a stream. The difference between sprintf and snprintf is that snprintf guarantees no buffer overrun by writing up to a maximum number of characters that can be stored in the buffer.

Use snprintf - it is standard an available in every compilator. Query it for the size needed by calling it with NULL, 0 parameters. Allocate one character more for null at the end.

int length = snprintf( NULL, 0, "%d", x );
char* str = malloc( length + 1 );
snprintf( str, length + 1, "%d", x );
...
free(str);

Better use sprintf(),

char stringNum[20];
int num=100;
sprintf(stringNum,"%d",num);