C Helper Functions

C has a large amount of helper libraries and functions.

stdlib.h

• char *getenv(const char *name) - Get environment variable
  • name - Name of the environment variable[4]
• long int strtol(const char *nptr, char **endptr, int base) - Converts a string into a long integer[1-2]
  • nptr - String to be read
  • endPtr - On success, points to first char after number; on failure, NULL
  • base - Base for number conversion
  • Returns converted number as long
• rand and srand - Random number generation[5]
  • void srand(unsigned int seed) - Set a seed for the pseudo-random number generator
  • int rand(void) - Return a pseudo-random number
  • e.g. srand(clock()); int num = rand();

stdio.h

• FILE *fopen(const char *path, const char *mode) - Open the file and return a stream of it.
  • path - To the file to be opened
  • mode - How the file should be opened
    • r / r+ - Open the file for reading / reading and writing, positioning the stream at the beginning of the file
    • w / w+ - Open file for writing / reading and writing, truncating file if it exists, creating file if it doesn't, positioning stream at beginning of the file
    • a / a+ - Open file for appending / reading and appending, creating file if it doesn't exist, positioning stream at the end of the file

References

1. https://linux.die.net/man/3/strtol
2. https://codeforwin.org/2018/01/convert-string-to-long-using-strtol-c.html
3. https://linux.die.net/man/3/fopen
4. https://www.tutorialspoint.com/c_standard_library/c_function_getenv.htm
5. https://linux.die.net/man/3/srand

Last modified: 202401040446