BCA Sem 1 | Unit 3 | Computer Concepts & C Programming
Overview of string.h Header File in C — BKNMU Junagadh
Detailed breakdown of string manipulation functions, length, copying, concatenation, comparison, and null-termination rules
'\0'). Since they are arrays, basic operators (like =, +, ==) cannot work directly on them. To handle common tasks like copying one string to another or comparing two strings, C provides a powerful standard library declared in #include <string.h>. This post provides a clear overview of these utilities for **BKNMU BCA Semester 1 (Unit 3)**.
The string.h library organizes predefined functions into four main categories, corresponding to the quadrants in your thumbnail:
1. String Length
Calculates the total number of characters in a string, strictly **excluding** the null terminator ('\0').
2. String Copy
Used to copy the complete contents of one source string character array into a destination character array.
3. String Concatenate
Used to physically join (append) the contents of one string to the end of another existing string.
4. String Compare
Used to check the lexicographical (alphabetical) relationship between two strings, returning integer results.
Here is a detailed breakdown of the primary functions supplied by the string.h standard library, detailing their parameters and behavior.
| Function Prototype | Functional Description | Input Parameters (Inputs) | Return Value (Output) |
|---|---|---|---|
size_t strlen(const char*) | Calculates the number of characters in the string, not including '\0'. | Pointer to the string character array. | Length of the string as a size_t integer. |
char* strcpy(char* dest, const char* src) | Copies the source string character array content into the destination array buffer. | Pointer to destination array (dest), Pointer to source string (src). | Pointer to the resulting destination string. |
char* strcat(char* dest, const char* src) | Appends the source string contents to the end of the destination string. | Pointer to destination string (dest), Pointer to source string (src). | Pointer to the resulting destination string. |
int strcmp(const char*, const char*) | Alphabetically compares two strings. Comparison is case-sensitive (ASCII value based). | Pointers to the two strings to compare. | Returns 0 if strings equal; Negative if Str1 < Str2; Positive if Str1 > Str2. |
char* strupr(char*) | Converts all lowercase alphabets in the given string to uppercase. *(Note: This function is non-standard ANSI C, but supported in Turbo C/BKNMU exams)* | Pointer to the string array. | Pointer to the updated uppercase string. |
'\0', ASCII 0). Without this character, string functions will continue reading memory indefinitely, causing crashes. Functions in string.h like strcpy and strcat automatically manage adding the null terminator.
1. Calculating Length using strlen():
#include <stdio.h>
#include <string.h> // Required for string functions
int main() {
char city[20] = "Junagadh";
int len;
// Calculates length, excluding '\0'
len = strlen(city);
printf("String: %s\n", city);
printf("Length of 'Junagadh' is: %d\n", len);
return 0;
}2. Using strcpy() and strcat() to Manipulate Strings:
#include <stdio.h>
#include <string.h>
int main() {
char src[20] = "Hello ";
char dest[40]; // Must have sufficient space
char add[10] = "World!";
// 1. Copy source string to destination
strcpy(dest, src);
printf("After strcpy: %s\n", dest); // Output: Hello
// 2. Concatenate (Append) third string to dest
strcat(dest, add);
printf("After strcat: %s\n", dest); // Output: Hello World!
return 0;
}3. Using strcmp() to Compare User Input:
#include <stdio.h>
#include <string.h>
int main() {
char user_pw[20] = "bca@knmu";
char input_pw[20];
printf("Enter Password: ");
scanf("%s", input_pw);
// Compare two strings case-sensitively
if (strcmp(user_pw, input_pw) == 0) {
printf("Access Granted!\n");
} else {
printf("Access Denied.\n");
}
return 0;
}Step 1: Locate First Character Address
The function call provides the base address (pointer) of the character array starting character.
Step 2: Sequential Memory Scan
The predefined function scans sequentially, char by char, through memory, performing its primary task (counting length, copying, comparing, or appending).
Step 3: Null Terminator Detection
Crucial Step! The scan stops ONLY when the null terminator ('\0') is detected. If copying, it also copies the '\0' to the destination.
strcmp() compares ASCII values.
- Returns 0 if Str1 == Str2
- Returns a NEGATIVE value if Str1 < Str2 (e.g., 'A' < 'B')
- Returns a POSITIVE value if Str1 > Str2 (e.g., 'Z' > 'Y')
strcpy and strcat, you must ensure the destination character array has **sufficient allocated memory** to hold the resulting joined/copied string PLUS the null terminator. Overflows lead to fatal segmentation faults!
- Statement Category: Standard Library Header (ansi c).
- Valid Inclusion Scope: Include via
#include <string.h>directive. - Primary Utilities: `strlen()`, `strcpy()`, `strcat()`, `strcmp()`, `strupr()`, `strlwr()`.
- Data Handling Rule: Most parameters and return types use pointers (
char*) and case-sensitive ASCII values. - Crucial Requirement: Must properly manage the null terminator (
'\0') in all custom implementations.