memcopying to a variable

[boddah]

Hi guys, I'm trying to copy the output from the for loop to a variable 'temp'

for(int i=1;i<4;i++)
{
printf("%s", 2 * i); //outputs - 246
}
printf("\n");

----------------------------------------------------------
I've tried this to only get 'segmentation fault'

char temp[20];
int a;
for(int i=0;i<10;i++)
{
printf("%d", 20 * i);
memcpy(temp[a], 2 * i, 1);
a++;
}
printf("\n");

---------------------------------------------------------
can anyone help me? Thanks

[donbock]

@boddah
With the "%s" format code you promise printf that you will pass it the pointer to a null-terminated string. Instead, you pass it an integer value. It will treat that integer value as a pointer and try to peer into memory at that address -- most likely something bad will happen.

@boddah
Good -- you're using the "%d" format string in printf. However, you are violating the function prototype for memcpy. You should have gotten compiler errors. If you're not, then perhaps you're not including <string.h>.

What are you trying to accomplish with the memcpy?

[weaknessforcats]

memcpy?

Why not just:

temp[i] = 2* i;

?

BTW: in your snippet the variable a is not initialized. Plus, your loop does not fill the entire array.

[boddah]

char temp[20];
int a=0;
for(int i=0;i<10;i++)
{
printf("%d", 20 * i);
memcpy(temp[a], 2 * i, 1);
a++;
}
Hi again. Sorry I forgot to include the initialization of a=0 in the 2nd snippet. Actually the for loop will printf an output of something like this printf("%c%c", <some formula here>);
the for loop doesn't iterate at a fixed num so I'm just initializing the temp[20] for testing purposes. What I'm trying to achieve are; while the for loop outputs the printf("%c%c,<formula>) -> outputting 2 characters each time it loops, I wish to put everything in 1 variable or 1 array of character. Hope that fills you in. Thanks

[newb16]

Use sprintf to create a string with a representation of a number, and strcpy to append it to your array.

[weaknessforcats]

That's fine, but why the memcpy?

A char is an integer. Your i is an integer. The calculation produces an integer. You assign your integer result to an integer.

Just assign the result to your array element. The compiler does the math for you.

You can assign temp[i] and temp[i+1] on the same loop cycle if you are trying to make your array look like your printf output.