C Library – stdlib.h

Posted in C Tutorial

Updated on Jun 02, 2024

By Mari Selvan

👁️ 21 - Views

⏳ 4 mins

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Photo Credit to CodeToFun

🙋 Introduction

The <stdlib.h> header file in the C programming language is a vital part of the standard library, providing a range of functions for performing general utility operations. These include memory allocation, process control, conversions, and other miscellaneous functions. Understanding the capabilities of <stdlib.h> is essential for effective C programming.

💡 Syntax

To use the functions and macros provided by <stdlib.h>, include the header file at the beginning of your C program:

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#include <stdlib.h>

📚 Key Functions and Macros

The following are the list of Memory Allocation Functions and macros

malloc():

Allocates a specified number of bytes and returns a pointer to the allocated memory.
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```
void *ptr = malloc(size_t size);
```
calloc():

Allocates memory for an array of elements, initializes them to zero, and returns a pointer to the memory.
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```
void *ptr = calloc(size_t num, size_t size);
```
realloc():

Resizes previously allocated memory.
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```
void *ptr = realloc(void *ptr, size_t size);
```
free():

Frees previously allocated memory.
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```
free(void *ptr);
```

The following are the list of Process Control Functions and macros

exit():

Terminates the calling process.
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```
void exit(int status);
```
abort():

Abnormally terminates the process.
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```
void abort(void);
```

The following are the list of Conversion functions and macros

atoi():

Converts a string to an integer.
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```
int num = atoi(const char *str);
```
atof():

Converts a string to a floating-point number.
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```
double num = atof(const char *str);
```

strtol():

Converts a string to a long integer.

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long int num = strtol(const char *str, char **endptr, int base);

strtod():

Converts a string to a double.
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```
double num = strtod(const char *str, char **endptr);
```

The following are the list of Miscellaneous Functions and macros

rand():

Returns a pseudo-random number.
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```
int random_number = rand(void);
```
srand():

Seeds the random number generator used by rand().
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```
void srand(unsigned int seed);
```

📝 Basic Example

Here's a complete example demonstrating the use of several <stdlib.h> functions:

example.c

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#include <stdio.h>
#include <stdlib.h>

int main() {
   // Memory allocation
   int *arr = (int *)malloc(5 * sizeof(int));
   if (arr == NULL) {
      fprintf(stderr, "Memory allocation failed\n");
      exit(1);
   }

   // Initialize array
   for (int i = 0; i < 5; i++) {
      arr[i] = i + 1;
   }

   // Print array elements
   for (int i = 0; i < 5; i++) {
      printf("%d ", arr[i]);
   }
   printf("\n");

   // Free allocated memory
   free(arr);

   // String to integer conversion
   char str[] = "12345";
   int num = atoi(str);
   printf("The integer value is %d\n", num);

   return 0;
}

💻 Output

Output

1 2 3 4 5 
The integer value is 12345

💰 Benefits

Using the <stdlib.h> library offers several benefits:

Versatility: Provides a wide range of functions that cover various aspects of programming, from memory management to process control and numerical conversions.
Standardization: As part of the C standard library, <stdlib.h> ensures that your code is portable and adheres to standard practices across different platforms and compilers.
Efficiency: The functions in <stdlib.h> are optimized for performance, which is crucial for developing efficient and responsive applications.
Ease of Use: The straightforward nature of the functions and macros in <stdlib.h> makes it accessible to both beginners and experienced programmers.
Robustness: Offers robust utilities for handling common programming tasks, reducing the likelihood of errors and improving code reliability.

🎉 Conclusion

The <stdlib.h> library in C is an indispensable resource for developers, providing essential functions for memory management, process control, conversions, and more.

Mastering the use of <stdlib.h> functions enhances your ability to write efficient, portable, and reliable C programs.