4.4 Strings

A C string is usually a character array ending with '\0'.

char word[6] = "hello";

The visible word has 5 characters, but one more slot is needed for the terminator '\0'.

Common string functions live in <string.h>:

• strlen() counts characters, not including '\0'.

• strcmp() compares two strings.

• strcpy() copies a string.

• strcat() concatenates strings.

When copying or concatenating, the destination array must have enough space. C will not grow it automatically.

To read a whole line into a string, use fgets(). It reads at most size - 1 characters and always adds a '\0' at the end, which makes it safer than scanf("%s"): it never writes past the buffer and it can read text that contains spaces.

#include <string.h>

char line[64];
fgets(line, sizeof(line), stdin);
line[strcspn(line, "\n")] = '\0';  // drop the trailing newline

fgets() keeps the newline the user typed, so a common step is to find it with strcspn() and replace it with '\0'.