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How to work with C strings

Updated September 2026 · Beginner-friendly guide

Understand termination

A C string is a character sequence ending in '\0'. The destination needs one extra byte for that terminator.

char word[] = "hello";
printf("%zu\n", sizeof word);  // 6 bytes

Use string functions

Include string.h. Use strlen only on a valid terminated string and strcmp rather than == to compare text.

if (strcmp(command, "quit") == 0) {
    printf("Goodbye\n");
}

Read a bounded line

fgets limits the write to the array size. Remove a trailing newline only if one was actually read.

char name[64];
if (fgets(name, sizeof name, stdin) != NULL) {
    name[strcspn(name, "\n")] = '\0';
}

Copy with a known capacity

Avoid strcpy and unbounded concatenation when input length is not proven. snprintf terminates when capacity is nonzero and reports the length it wanted to write.

char label[32];
int needed = snprintf(label, sizeof label, "User: %s", name);
if (needed < 0 || (size_t) needed >= sizeof label) {
    fprintf(stderr, "Label was too long.\n");
}

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