fgets()

Don't use gets()!

char *
fgets(char * restrict str, int size, FILE * restrict stream);

The right usage:

fgets(str, sizeof (str), stdin);

Example:

char str[10];
printf("Name [%d]? ", sizeof (str));
fgets(str, sizeof (str), stdin);
printf("Hello, %s!\n", str);

snprintf()

Don't use sprintf()!

int
snprintf(char * restrict str, size_t size, const char * restrict format, ...);

The right usage:

snprintf(str, sizeof (str), format, ...);

Example:

char str[5];
char *format = "%02x%02x%02x";
snprintf(str, sizeof (str), format, 'B', 'S', 'D'); /* "4253\0" */

strncat()

char *
strncat(char * restrict s, const char * restrict append, size_t count);

The right usage:

strncat(s, append, sizeof (s) - strlen(s) - 1);

Example:

char s[] = {'F', 'r', 'e', 'e', '\0', '*', '*'};
char *append = "BSD";
strncat(s, append, sizeof (s) - strlen(s) - 1); /* "FreeBS\0" */

strlcat()

size_t
strlcat(char *dst, const char *src, size_t size);

The right usage:

strlcat(dst, src, sizeof (dst));

Example:

char dst[] = {'F', 'r', 'e', 'e', '\0', '*', '*'};
char *src = "BSD";
strlcat(dst, src, sizeof (dst)); /* "FreeBS\0" */

strncpy()

char *
strncpy(char * restrict dst, const char * restrict src, size_t len);

The right usage:

strncpy(dst, src, sizeof (dst) - 1);
dst[sizeof (dst) - 1] = '\0';

Example:

char dst[] = {'*', '*', '*', '*', '*'};
char *src = "HELLO";
strncpy(dst, src, sizeof (dst) - 1); /* "HELL*" */
dst[sizeof (dst) - 1] = '\0';        /* "HELL\0" */

strlcpy()

size_t
strlcpy(char *dst, const char *src, size_t size);

The right usage:

strlcpy(dst, src, sizeof (dst));

Example:

char dst[] = {'*', '*', '*', '*', '*'};
char *src = "HELLO";
strlcpy(dst, src, sizeof (dst)); /* "HELL\0" */

Test for strncpy() and strlcpy()

The dst is:

char dst[5];

The dot symbol shows where data is unchanged.