I'm trying to make a simple program where parts of other strings are appended to another string. When I run this code, it doesn't output anything. Sorry, my C knowledge is very low. All help appreciated.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
char stuff[100] = "Y";
char test[] = "hello", test2[] = "shelllo";
strcat(stuff, test[1]);
strcat(stuff, test2[0]);
printf("%s\n", stuff);
return 0;
}
You need to remove array index from your strcat which should look like:
strcat(stuff, test);
strcat(stuff, test2);
Note that test and test2 are strings, but test[1] and test2[0] are just individual characters (e and s) - strcat works with string, not individual characters.
If you want to copy just part of a string (ie skipping first few characters), then use pointer arithmetic
strcat(stuff, test + 1); // skip 1st character of test (ie start copying from `e`)
or,
strcat(stuff, test2 + 3); // skip 3 characters of test2 (ie starting copying from `l`)
You are calling strcat with a char argument instead of a pointer to char, the behavior is undefined.
Here are solutions to copy portions of strings:
strncat(): it copies no more than a given number of characters to the end of its first argument.snprintf() with the %.*s format. The precision field for the %s format specifies the maximum number of characters to copy from the string. It can be specified as a decimal number or as a * in which case the precision is passed as an int argument before the string argument.Here is an example:
#include <stdio.h>
#include <string.h>
int main(void) {
char stuff[100];
char test[] = "Hello";
char test2[] = "The world is flat";
/* using strncat */
strcpy(stuff, test);
strncat(stuff, test2 + 3, 6);
printf("%s\n", stuff);
/* safer version using snprintf */
snprintf(stuff, sizeof stuff, "Hello %.*s\n", 5, test2 + 4);
printf("%s\n", stuff);
return 0;
}
%.* does would be good - it's not commonly used
snprintf is safer because one can pass the size of the destination array so snprintf will not cause a buffer overflow. strncat does not have this information, it is up to the programmer to check if there is enough space at the end of the string in the destination array for the concatenated substring. A notoriously more risky option.