C standard library functions are one of the most important and useful topics in the C programming language. Without standard C library functions, you cannot execute a program in C. These functions are provided by the system and then stored in the library.<\/p>\n
These functions are also known as built-in functions in C. And these functions are stored in a common collection called a library. Each function provides a different operation. With the help of these standard functions, a programmer can get the desired output of his\/her program easily.<\/p>\n
During the time of designing compilers, these library functions are created.<\/p>\n
1. Usability:-<\/strong> One of the important advantages of using these functions is that it will allow a programmer to use the pre-existing code available in the C compiler. These library functions are easy to use.<\/p>\n 2. Optimization:-<\/strong> A group of developers always make sure that these standard library functions are up to date. And they are also making efficient code that will optimize the performance.<\/p>\n 3. Portable:-<\/strong> You can use these standard library functions anytime and anywhere. They are platform-independent.<\/p>\n 4. Time Saving:-<\/strong> If you have to find a square root and print the output on the screen then you don\u2019t have to write numerous lines of code. With the help of standard C library functions, you can do this type of work easily.<\/p>\n 5. User-Friendly Syntax:-<\/strong> In C, the syntax of these library functions is easy to understand and implement.<\/p>\n 6. Flexibility:-<\/strong> A programmer can easily modify their code or program with the help of standard library functions.<\/p>\n You can use these standard C library functions by declaring header files. Different header files include different functions and different operations.<\/p>\n Below is the list of header files in C:-<\/p>\n Below are the header files in detail.<\/p>\n A programmer has to put this header file in every program. This is a basic header file in C. This header file mainly used to perform input and output functions like:-<\/p>\n Example of stdio.h in C<\/strong><\/p>\n Output<\/strong><\/p>\n This header file is used to perform dynamic allocations through malloc(), calloc(), free(), realloc().<\/p>\n It is used for dynamic allocation in C. It is mainly used for allocating a block of memory dynamically. And it returns a null pointer during the execution of the program.<\/p>\n Syntax of C Malloc Function<\/strong><\/p>\n Example<\/strong><\/p>\n Example:- malloc() function<\/strong><\/p>\n Output<\/strong><\/p>\n Calloc stands for Contiguous allocation. The main purpose of this is to allocate multiple blocks of memory. This function is used for allocating memory to complex data structures like arrays, structures etc.<\/p>\n Syntax of C Calloc Function<\/strong><\/p>\n Example of Calloc Function in C<\/strong><\/p>\n Example of C calloc() function<\/strong><\/p>\n Output<\/strong><\/p>\n It is used to deallocate or release memory in C programs. During dynamic allocation, you have to free some memory explicitly. If not, you may encounter errors in compilation.<\/p>\n Syntax:-<\/strong><\/p>\n Example:-<\/strong><\/p>\n Example:- free() function<\/strong><\/p>\n Output<\/strong><\/p>\n It is used for allocating more memory to the already allocated memory. realloc() stands for reallocation of memory.<\/p>\n Syntax:-<\/strong><\/p>\n Example:-<\/strong><\/p>\n Example:- free() function<\/strong><\/p>\n Output<\/strong><\/p>\n NOTE:-<\/strong> If you want to use the above mentioned functions then you have to include <stdlib.h><\/strong> header file in your program code.<\/p>\n This header file will let you perform some mathematical operations in your program. This header file includes functions such as:-<\/p>\n Example:-<\/strong> <math.h> header file<\/strong><\/p>\n Output<\/strong><\/p>\n TechVidvan Tutorials: <math.h> header file examples!<\/p>\n Square root of 4 is: 2 NOTE:-<\/strong> If you want to use the above mentioned functions then you have to include <math.h><\/strong> header file in your program code.<\/p>\n This header file includes functions which will help you in character handling. The <ctype.h><\/strong> header file has functions such as:-<\/p>\n Example:- <ctype.h> header file<\/strong><\/p>\n Output<\/strong><\/p>\n NOTE:-<\/strong> You have to include \u201c#include <ctype.h><\/strong>\u201d to run the above character handling functions.<\/p>\n This header file has functions which will help in handling and manipulating strings in your program code.<\/p>\n <string.h> header file has functions such as:-<\/p>\nHeader files in C<\/h3>\n
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\n Header File<\/b><\/td>\n What it does<\/b><\/td>\n<\/tr>\n \n stdio.h<\/span><\/td>\n Mainly used to perform input and output operations like print(), scanf().<\/span><\/td>\n<\/tr>\n \n string.h<\/span><\/td>\n Mainly used to perform string handling operations like strlen(), strcmp() etc.<\/span><\/td>\n<\/tr>\n \n conio.h<\/span><\/td>\n Used to perform console input and output operations.<\/span><\/td>\n<\/tr>\n \n stdlib.h<\/span><\/td>\n Mainly used to perform standard utility functions like malloc(), calloc() etc.<\/span><\/td>\n<\/tr>\n \n math.h<\/span><\/td>\n Mainly used to perform mathematical operations like sqrt(), pow() etc.<\/span><\/td>\n<\/tr>\n \n ctype.h<\/span><\/td>\n Used to perform character type functions like isdigit(), isalpha() etc.<\/span><\/td>\n<\/tr>\n \n time.h<\/span><\/td>\n Used to perform operations related to date and time.<\/span><\/td>\n<\/tr>\n \n assert.h<\/span><\/td>\n Used to verify assumptions made by a program and print a message if the assumption is false using functions like assert() etc.<\/span><\/td>\n<\/tr>\n \n locale.h<\/span><\/td>\n Mainly used to perform localization like functions such as setlocale() etc.<\/span><\/td>\n<\/tr>\n \n signal.h<\/span><\/td>\n Mainly used to perform signal handling functions such as signal(), raise() etc.<\/span><\/td>\n<\/tr>\n \n setjmp.h<\/span><\/td>\n Used to perform jump functions.<\/span><\/td>\n<\/tr>\n \n stdarg.h<\/span><\/td>\n Used to perform standard argument functions like va_start() etc.<\/span><\/td>\n<\/tr>\n \n errno.h<\/span><\/td>\n For performing error handling operations such as errno() to indicate the errors.<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n stdio.h<\/h4>\n
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#include <stdio.h>\nint main() {\n char name[20]=\"TechVidvan\";\n printf(\"Tutorial name is: %s\\n\",name);\n int age;\nprintf(\"Enter your age: \\n\");\n scanf(\"%d\",&age);\n printf(\"Your age is: %d\\n\",age);\n return 0;\n}\n<\/pre>\n
\nEnter your age:
\nYour age is: 20<\/div>\n<stdlib.h> header file<\/h4>\n
malloc function in C:-<\/h4>\n
pointer_name = (cast_type *) malloc (byte_size);<\/pre>\n
pointer = malloc(int *) malloc(10 * sizeof(int));\n<\/pre>\n
#include <stdlib.h>\n#include <stdio.h>\nint main(){\nint *point;\npoint = malloc(10 * sizeof(*point)); \/\/ block of 15 integers!\n*(point + 1) = 10; \/* assign 480 to sixth integer *\/\nprintf(\"Value of second integer is %d\",*(point + 1));\n}\n<\/pre>\ncalloc() function in C<\/h4>\n
pointer = (cast_type *) calloc (no_of_bytes, size_of_cast_type);<\/pre>\n
pointer = calloc(4, sizeof(int));\n<\/pre>\n
#include <stdio.h>\n#include <stdlib.h>\nint main() {\nint a, *point, sum = 0;\npoint = calloc(4, sizeof(int));\nprintf(\"TechVidvan Tutorial: calloc() function!\\n\");\nprintf(\"Sum of first 4 terms!\\n\");\nfor (a=0;a<4;a++) {\n*(point + a) = a;\nsum = sum + *(point + a);\n}\nprintf(\"Sum is: %d\", sum);\nreturn 0;\n}\n<\/pre>\n
\nSum of first 4 terms!
\nSum is: 6<\/div>\nfree() function in C<\/h4>\n
free(name_of_pointer);<\/pre>\n
free(point);<\/pre>\n
#include <stdio.h>\n#include <stdlib.h>\nint main() {\nint *point = malloc(4 * sizeof(*point));\n*(point + 3) = 5;\nprintf(\"Third integer value is: %d\",*(point + 3));\nfree(point);\n}\n<\/pre>\nrealloc() function in C<\/h4>\n
point = realloc(point, new_sizeof())<\/pre>\n
point = (int*) malloc(4 * sizeof(int));\npoint = realloc(point, 6 * sizeof(int));\n<\/pre>\n
include <stdio.h>\n#include <stdlib.h>\n#include <string.h>\nint main () {\nchar *string_name;\nstring_name = (char *) malloc(20);\nstrcpy(string_name, \"TechVidvan\");\nstring_name = (char *) realloc(string_name, 30); \/\/ Reallocating memory\nstrcat(string_name, \" Tutorials!\");\nprintf(\"Favourite website for C tutorials is: %s\", string_name);\nreturn(0);\n}\n<\/pre>\n<math.h> header file<\/h4>\n
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#include <stdio.h>\n#include <math.h>\nint main()\n{\nprintf(\"TechVidvan Tutorials: <math.h> header file examples!\\n\\n\");\nint num=4, squareRoot;\nint power = 3, result_of_power;\ndouble num1 = -7.2, res;\ndouble tan_res;\nsquareRoot = sqrt(num);\nprintf(\"Square root of %d is: %d\\n\", num, squareRoot);\nresult_of_power = pow(num,power);\nprintf(\"Power of %d is: %d\\n\",num,result_of_power);\nres = fabs(num1);\nprintf(\"Absolute value of %f is: %d\\n\",num1,res);\ntan_res = tan(num);\nprintf(\"Tangent value of %d is: %f\",num,tan_res);\nreturn 0;\n}\n<\/pre>\n
\nPower of 4 is: 64
\nAbsolute value of -7.200000 is: 0
\nTangent value of 4 is: 1.157821<\/p>\n<\/div>\n<ctype.h> header file<\/h4>\n
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#include <stdio.h>\n#include <ctype.h>\nint main()\n{\nprintf(\"TechVidvan Tutorials: <ctype.h> header file examples!\\n\\n\");\nchar a,res;\nchar b,c;\na='T';\nb = 't';\nc = '7';\nprintf(\"Converting %c to lower case: %c\\n\",a,tolower(a));\nif(isalpha(a)){\n printf(\"It is a character!\\n\");\n}\nif(isdigit(a)){\n printf(\"It is a digit!\\n\");\n}\nelse{\n printf(\"It is not digit!\\n\");\n}\nif(isalnum(c)){\n printf(\"It is alphanumeric!\\n\");\n}\nprintf(\"Converting %c to upper case: %c\\n\",b,toupper(b));\nreturn 0;\n}\n<\/pre>\n
\nIt is a character!
\nIt is not digit!
\nIt is alphanumeric!
\nConverting t to upper case: T<\/div>\n<string.h> header file<\/h4>\n
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