Lesson 10.3. The string.h library

The string.h library is a standard C library. It contains various functions for string manipulation. This page presents some of the most frequently used ones, but this presentation is not exhaustive.

#include <string.h>

Length of a string

The strlen() function that we have already used in this course returns the number of characters (up to the zero at the end of the string).

size_t strlen(const char *);

Copy a string

The strcpy() function (string copy) copies the source string to the destination string. Be careful, the destination string must be large enough to accommodate the copy. The characters are copied up to the null character.

char *strcpy(char *destination, const char *source);

String comparison

The strcmp() function (string compare) compares two strings. The function returns 0 if the strings are identical, a non-zero value otherwise.

int strcmp(const char *s1, const char *s2);

String concatenation

A string concatenation is the operation of joining strings end-to-end.

The function strcat() (string concatenate) adds the string source to the end of the string destination. As for the strcpy() function, it is necessary that the destination string must be large enough to accommodate the two strings end-to-end.

char * strcat ( char * destination, const char * source );

Exercises

Exercise 1

Write a program that asks the user to enter his first name (50 characters maximum), then his last name (50 characters maximum). Then, the program creates and displays a string message that contains the text "Hello First Name Last Name.".

The program must create a string with the full name before displaying it. In other words, you have to use a function from the string.h library.

For example:

First name : Justin
Last name : Case
Hello Justin Case

#include <stdio.h> #include <string.h> int main(void) { // Create strings // COMPLETE HERE // Ask for first and last name printf("First name : "); scanf("%50s", firstname); printf("Last name : "); scanf("%50s", lastname); // Concatenate (mandatory) // COMPLETE HERE // Display the final string printf("%s\n", message); return 0; }

Exercise 2

We provide the following strings:

#define   TEXT  "Text to copy."

char src[] = TEXT;
char dest[] = "String for the copy.";

Write the code that copies the string str into the string dest, then check that the copy is equal to TEXT. If the copy was successful, the program displays the program displays Copy OK, otherwise it displays Copy error.

Copy OK

#include <stdio.h> #include <string.h> #define TEXT "Text to copy." int main(void) { char src[] = TEXT; char dest[] = "String for the copy."; // Copy src => dest // COMPLETE HERE // Check the copy // COMPLETE HERE return 0; }

Quiz

The string.h library...

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The strcpy() function ...

char *strcpy(char *s1, const char *s2);

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The strcat() function ...

char *strcat(char *s1, const char *s2);

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With the strcat() and strcpy() functions, the size of the destination string ...

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See also

• Learn C programming
• Lesson 1.1. History of C programming language
• Lesson 1.2. First program
• Lesson 1.3. Compilation
• Lesson 1.4. Preprocessor directives
• Lesson 1.5. Which compiler to choose?
• Lesson 1.6. Flowchart
• Lesson 2.1. Types and variables
• Lesson 2.2. Integers
• Lesson 2.3. Floating point numbers
• Lesson 2.4. Characters
• Lesson 2.5. Variables initialization
• Lesson 2.6. Ariane flight 501
• Lesson 3.1. Arithmetic operators
• Lesson 3.2. modulo
• Lesson 3.3. Operators and types
• Lesson 3.4. Type casting
• Lesson 3.5. Bitwise operators
• Lesson 3.6. Bitwise operators details
• Lesson 3.7. Shifting operators
• Lesson 3.8. Assignment operators
• Lesson 3.9. Increment and decrement operators
• Lesson 3.10. Comparison operators
• Lesson 3.11. Logical operators
• Lesson 3.12. Operator precedence
• Lesson 4.1. printf
• Lesson 4.2. scanf
• Lesson 4.3. putchar
• Lesson 5.1. Conditional branching (if...else)
• Lesson 5.2. Nested if and indentation
• Lesson 5.3. Checking intervals
• Lesson 5.4. Ternary Operator ?:
• Lesson 5.5. switch..case statement
• Lesson 5.6. Break keyword in switch..case
• Lesson 6.1. do..while loop in C
• Lesson 6.2. While loop in C
• Lesson 6.3. For loop in C
• Lesson 6.4. How to choose the right loop in C ?
• Lesson 6.5. Exercices on loops in C
• Lesson 7.1. Bit masking
• Lesson 7.2. Bit masking, how to clear a bit in C?
• Lesson 7.3. Bit masking, how to set a bit in C?
• Lesson 7.4. Bit masking, how to toggle a bit in C?
• Lesson 7.5. Bit masking, how to check a single bit in C?
• Lesson 7.6. Overview of bit masking
• Lesson 8.1. Basic syntax of C functions
• Lesson 8.2. Calling C functions
• Lesson 8.3. Void keyword
• Lesson 8.4. Return keyword
• Lesson 8.5. Variable scope
• Lesson 8.6. Global variables
• Lesson 8.7. Static variables
• Lesson 8.8. Random numbers in C
• Lesson 8.9. Mathematical functions in C
• Lesson 9.1. Syntax of C arrays
• Lesson 9.2. Array initialization
• Lesson 9.3. Multidimensional arrays
• Lesson 9.4. How C arrays are stored in memory?
• Lesson 9.5. Arrays and functions
• Lesson 9.6. Exercises on C arrays
• Lesson 10.1. Strings in C
• Lesson 10.2. Null terminated string
• Lesson 10.4. String and functions
• Lesson 11.1. Introduction to pointers in C
• Lesson 11.2. Syntax of C pointers
• Lesson 11.3. Dynamic memory allocation
• Lesson 11.4. Incrementing pointers
• Lesson 11.5. Pointers as function argument in C
• Lesson 12.1. Introduction to structures in C
• Lesson 12.2. Properties of structures in C
• Lesson 12.3. Structures and pointers
• Lesson 12.4. Structures and functions
• Lesson 13.1. Recursive functions in C
• Lesson 13.2. Depth of recursive functions
• Lesson 13.2. Mutual recursion
• Lesson 14.1. Additional exercises

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