The "Essential" Standard Functions

In a professional C or embedded environment, we call these Standard Library Functions. While you won't use printf inside a car's braking system (because there is no screen to print to!), you will use it constantly during testing and debugging on your PC or through a UART console.

A close-up view of a microcontroller circuit board showcasing its intricate design.

Here is the "Essential List" of functions every embedded engineer should know by heart.

​1. Input / Output Functions (stdio.h)

​printf (Print Formatted)

• ​What it does: Sends a formatted string to the "Standard Output" (usually your console).

• ​Syntax: int printf(const char *format, ...);

• ​Returns: The total number of characters printed. If it fails, it returns a negative number.

​scanf (Scan Formatted)

• ​What it does: Reads input from the keyboard/console and stores it in variables.

• ​Syntax: int scanf(const char *format, ...);

• ​Returns: The number of items successfully read and assigned.

• ​Corporate Warning: We rarely use scanf in real products because it is "blocking" (it stops everything until you type) and unsafe if the user types too much data.

​2. String Manipulation (string.h)

​strlen (String Length)

• ​What it does: Counts how many characters are in a string (not counting the null terminator \0).

• ​Syntax: size_t strlen(const char *str);

• ​Returns: The number of characters (as an unsigned integer).

​strcpy (String Copy)

• ​What it does: Copies a "Source" string into a "Destination" buffer.

• ​Syntax: char strcpy(char dest, const char *src);

• ​Returns: A pointer to the destination string.

• ​Safety Tip: In the industry, we prefer strncpy because it lets us set a limit so we don't crash the memory (Buffer Overflow).

​strcmp (String Compare)

• ​What it does: Compares two strings alphabetically.

• ​Syntax: int strcmp(const char str1, const char str2);

• ​Returns: * 0 if they are identical.

  • ​Positive if str1 is "greater."

  • ​Negative if str2 is "greater."

​3. Memory Operations (string.h)

​Note: These are the "Workhorses" of Embedded C.

​memset (Memory Set)

• ​What it does: Fills a block of memory with a specific value.

• ​Example: Clearing a sensor data array to all zeros.

• ​Syntax: void memset(void ptr, int value, size_t num);

• ​Returns: A pointer to the memory area.

​memcpy (Memory Copy)

• ​What it does: Copies a block of raw bytes from one place to another.

• ​Example: Moving a packet of SPI data into a processing buffer.

• ​Syntax: void memcpy(void dest, const void *src, size_t num);

• ​Returns: A pointer to the destination.

​4. General Utilities (stdlib.h)

​abs / labs (Absolute Value)

• ​What it does: Turns a negative number into a positive one. Very useful for sensor error calculations.

• ​Syntax: int abs(int n);

• ​Returns: The positive value of the integer.

​atoi (Alpha to Integer)

• ​What it does: Converts a string (like "123") into an actual number (123).

• ​Syntax: int atoi(const char *str);

• ​Returns: The converted integer.

Summary Reference Table

Function	Library	Purpose	Key Return
printf	stdio.h	Output text	Character count
strlen	string.h	Get string size	Length
memset	string.h	Zero-out/Fill memory	Pointer to start
memcpy	string.h	Copy raw data blocks	Pointer to start
strcmp	string.h	Check if strings match	0 if equal

Professor's Challenge:

​In your AUTOSAR/Jacinto testing, you will likely use memcpy to move data from the SPI Internal Buffer to your Test Report buffer.