String Helper Functions

let’s do a quick recap of important C string helper functions from <string.h>. These are the ones you’ll actually use a lot in firmware / interviews.

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1. String Length

size_t strlen(const char *str);

Returns length of string (not counting \0).

char s[] = "Hello";
printf("%zu\n", strlen(s));  // 5

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2. Copying Strings

char *strcpy(char *dest, const char *src);
char *strncpy(char *dest, const char *src, size_t n);

strcpy copies whole string, strncpy limits to n chars.

char src[] = "World";
char dest[10];
strcpy(dest, src);   // dest = "World"

Be careful: strcpy can overflow buffer. Use strncpy for safety.

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3. Concatenation

char *strcat(char *dest, const char *src);
char *strncat(char *dest, const char *src, size_t n);

Appends src to dest.

char s[20] = "Hello ";
strcat(s, "World");  // s = "Hello World"

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4. Comparison

int strcmp(const char *s1, const char *s2);
int strncmp(const char *s1, const char *s2, size_t n);

Returns 0 if equal, <0 if s1<s2, >0 if s1>s2.

printf("%d\n", strcmp("abc","abc")); // 0
printf("%d\n", strcmp("abc","abd")); // -1

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5. Search

• Find first occurrence of character:

char *strchr(const char *str, int c);

char *p = strchr("hello", 'e'); // points to "ello"

• Find last occurrence of character:

char *strrchr(const char *str, int c);

• Find substring:

char *strstr(const char *haystack, const char *needle);

char *p = strstr("hello world", "world"); // points to "world"

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6. Tokenize

char *strtok(char *str, const char *delim);

Splits string into tokens.

char s[] = "red,green,blue";
char *token = strtok(s, ",");
while (token != NULL) {
    printf("%s\n", token);
    token = strtok(NULL, ",");
}

Output:

red
green
blue

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7. Memory Helpers

These work on raw memory, not just strings:

void *memcpy(void *dest, const void *src, size_t n);
void *memmove(void *dest, const void *src, size_t n);
void *memset(void *str, int c, size_t n);
int memcmp(const void *s1, const void *s2, size_t n);

• memcpy – fast copy (no overlap).
• memmove – safe copy (handles overlap).
• memset – fill memory with value.
• memcmp – compare memory blocks.

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Quick Tricks:

• Use strlen + strcpy/strncpy to duplicate.
• Use strtok to parse UART strings / CSV.
• Use memset to clear structs (memset(&myStruct, 0, sizeof(myStruct))).
• Use strstr to detect commands (if (strstr(rxBuffer, "START")) { ... }).

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