All functions
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This document lists and describes 143 C functions. It groups the functions into categories such as string manipulation, preprocessor directives, mathematical functions, file handling, and more. Some key functions include printf() for formatted output, scanf() for formatted input, strcpy() to copy strings, atoi() to convert strings to integers, and exit() to terminate a program.
All functions
- 1. All C Functions 1. #, ## manipulate strings 2. #define define variables 3. #error display an error message 4. #if, #ifdef, #ifndef, #else, #elif, #endif conditional operators 5. #include insert the contents of another file 6. #line set line and file information 7. #pragma implementation specific command 8. #undef used to undefine variables 9. Predefined preprocessor variables miscellaneous preprocessor variables 10. abort stops the program 11. abs absolute value 12. acos arc cosine 13. asctime a textual version of the time 14. asin arc sine 15. assert stops the program if an expression isn't true 16. atan arc tangent 17. atan2 arc tangent, using signs to determine quadrants 18. atexit sets a function to be called when the program exits 19. atof converts a string to a double 20. atoi converts a string to an integer 21. atol converts a string to a long 22. bsearch perform a binary search 23. calloc allocates and clears a two-dimensional chunk of memory 24. ceil the smallest integer not less than a certain value 25. clearerr clears errors 26. clock returns the amount of time that the program has been running 27. cos cosine 28. cosh hyperbolic cosine
- 2. 29. ctime returns a specifically formatted version of the time 30. difftime the difference between two times 31. div returns the quotient and remainder of a division 32. exit stop the program 33. exp returns "e" raised to a given power 34. fabs absolute value for floating-point numbers 35. fclose close a file 36. feof true if at the end-of-file 37. ferror checks for a file error 38. fflush writes the contents of the output buffer 39. fgetc get a character from a stream 40. fgetpos get the file position indicator 41. fgets get a string of characters from a stream 42. floor returns the largest integer not greater than a given value 43. fmod returns the remainder of a division 44. fopen open a file 45. fprintf print formatted output to a file 46. fputc write a character to a file 47. fputs write a string to a file 48. fread read from a file 49. free returns previously allocated memory to the operating system 50. freopen open an existing stream with a different name 51. frexp decomposes a number into scientific notation 52. fscanf read formatted input from a file 53. fseek move to a specific location in a file 54. fsetpos move to a specific location in a file 55. ftell returns the current file position indicator 56. fwrite write to a file 57. getc read a character from a file 58. getchar read a character from STDIN 59. getenv get enviornment information about a variable 60. gets read a string from STDIN
- 3. 61. gmtime returns a pointer to the current Greenwich Mean Time 62. isalnum true if a character is alphanumeric 63. isalpha true if a character is alphabetic 64. iscntrl true if a character is a control character 65. isdigit true if a character is a digit 66. isgraph true if a character is a graphical character 67. islower true if a character is lowercase 68. isprint true if a character is a printing character 69. ispunct true if a character is punctuation 70. isspace true if a character is a space character 71. isupper true if a character is an uppercase character 72. isxdigit true if a character is a hexidecimal character 73. labs absolute value for long integers 74. ldexp computes a number in scientific notation 75. ldiv returns the quotient and remainder of a division, in long integer form 76. localtime returns a pointer to the current time 77. log natural logarithm 78. log10 natural logarithm, in base 10 79. longjmp start execution at a certain point in the program 80. malloc allocates memory 81. memchr searches an array for the first occurance of a character 82. memcmp compares two buffers 83. memcpy copies one buffer to another 84. memmove moves one buffer to another 85. memset fills a buffer with a character 86. mktime returns the calendar version of a given time 87. modf decomposes a number into integer and fractional parts 88. perror displays a string version of the current error to STDERR 89. pow returns a given number raised to another number 90. printf write formatted output to STDOUT 91. putc write a character to a stream
- 4. 92. putchar write a character to STDOUT 93. puts write a string to STDOUT 94. qsort perform a quicksort 95. raise send a signal to the program 96. rand returns a pseudorandom number 97. realloc changes the size of previously allocated memory 98. remove erase a file 99. rename rename a file 100. rewind move the file position indicator to the beginning of a file 101. scanf read formatted input from STDIN 102. setbuf set the buffer for a specific stream 103. setjmp set execution to start at a certain point 104. setlocale sets the current locale 105. setvbuf set the buffer and size for a specific stream 106. signal register a function as a signal handler 107. sin sine 108. sinh hyperbolic sine 109. sprintf write formatted output to a buffer 110. sqrt square root 111. srand initialize the random number generator 112. sscanf read formatted input from a buffer 113. strcat concatenates two strings 114. strchr finds the first occurance of a character in a string 115. strcmp compares two strings 116. strcoll compares two strings in accordance to the current locale 117. strcpy copies one string to another 118. strcspn searches one string for any characters in another 119. strerror returns a text version of a given error code 120. strftime returns individual elements of the date and time 121. strlen returns the length of a given string 122. strncat concatenates a certain amount of characters of two strings 123. strncmp compares a certain amount of characters of two strings
- 5. 124. strncpy copies a certain amount of characters from one string to another 125. strpbrk finds the first location of any character in one string, in another string 126. strrchr finds the last occurance of a character in a string 127. strspn returns the length of a substring of characters of a string 128. strstr finds the first occurance of a substring of characters 129. strtod converts a string to a double 130. strtok finds the next token in a string 131. strtol converts a string to a long 132. strtoul converts a string to an unsigned long 133. strxfrm converts a substring so that it can be used by string comparison functions 134. system perform a system call 135. tan tangent 136. tanh hyperbolic tangent 137. time returns the current calendar time of the system 138. tmpfile return a pointer to a temporary file 139. tmpnam return a unique filename 140. tolower converts a character to lowercase 141. toupper converts a character to uppercase 142. ungetc puts a character back into a stream 143. va_arg use variable length parameter lists 144. vprintf, vfprintf, and vsprintf write formatted output with variable argument lists