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840Testing for alphabetic characters with `isalpha`
841Checking for digits with `isdigit` and `isxdigit`
842Identifying whitespace with `isspace`
843Distinguishing `ispunct` and `isgraph`
844Case testing with `isupper` and `islower`
845Converting case with `toupper` and `tolower`
846The importance of casting to `unsigned char` in `ctype` functions
847Finding string length with `strlen`
848Copying strings safely with `strncpy`
849Concatenating strings with `strncat`
850Lexicographical comparison with `strcmp`
851Searching for characters with `strchr` and `strrchr`
852Finding substrings with `strstr`
853Tokenizing strings with `strtok`
854Understanding the `strcoll` and `strxfrm` locale functions
855Setting memory blocks with `memset`
856Copying memory with `memcpy`
857Handling overlapping regions with `memmove`
858Comparing memory blocks with `memcmp`
859Searching memory bytes with `memchr`
860Performance differences between `str` and `mem` functions
861Basic power and square root: `pow` and `sqrt`
862Exponential and logarithmic functions: `exp`, `log`, `log10`
863Trigonometric functions in radians
864Rounding with `ceil`, `floor`, and `round`
865Truncation and remainder: `trunc` and `fmod`
866Absolute values for floats with `fabs`
867Handling `NAN` and `INFINITY` constants
868Allocating memory with `malloc` and `free`
869Contiguous allocation with `calloc`
870Resizing blocks with `realloc`
871Converting strings to integers with `atoi` and `atol`
872Robust string-to-number conversion with `strtol`
873Converting strings to doubles with `strtod`
874Communicating with the OS using `system`
875Cleaning up at exit with `atexit`
876The generic signature of `qsort`
877Writing an integer comparison function
878Writing a string comparison function for `qsort`
879Sorting structs by multiple fields
880Using `bsearch` on sorted arrays
881Handling the `void*` return of `bsearch`
882Common pitfalls in comparison function logic
883Generating pseudo-random numbers with `rand`
884The importance of the `RAND_MAX` constant
885Seeding the generator with `srand`
886Why you should only seed once
887Scaling `rand` results to a specific range
888Getting a unique seed with `time(NULL)`
889Getting system time with `time_t`
890Measuring intervals with `difftime`
891Breaking down time with `struct tm`
892Converting `time_t` to local time with `localtime`
893Converting `time_t` to UTC with `gmtime`
894Formatting time strings with `strftime`
895Converting `struct tm` back to `time_t` with `mktime`
896Measuring CPU ticks with `clock`
897The global `errno` variable
898Interpreting errors with `perror`
899Getting error strings with `strerror`
900Resetting `errno` before library calls
901Using `assert` for internal debugging
902Disabling assertions with `NDEBUG`
903When to use `errno` vs return codes
904Integer ranges in `limits.h`
905Using `INT_MAX` and `INT_MIN` for overflow checks
906Platform-specific character sizes
907Precision and epsilon in `float.h`
908Checking `FLT_DIG` and `DBL_DIG` for precision limits
909Managing large constants: `LONG_MAX` vs `LLONG_MAX`

840Testing for alphabetic characters with `isalpha`
841Checking for digits with `isdigit` and `isxdigit`
842Identifying whitespace with `isspace`
843Distinguishing `ispunct` and `isgraph`
844Case testing with `isupper` and `islower`
845Converting case with `toupper` and `tolower`
846The importance of casting to `unsigned char` in `ctype` functions
847Finding string length with `strlen`
848Copying strings safely with `strncpy`
849Concatenating strings with `strncat`
850Lexicographical comparison with `strcmp`
851Searching for characters with `strchr` and `strrchr`
852Finding substrings with `strstr`
853Tokenizing strings with `strtok`
854Understanding the `strcoll` and `strxfrm` locale functions
855Setting memory blocks with `memset`
856Copying memory with `memcpy`
857Handling overlapping regions with `memmove`
858Comparing memory blocks with `memcmp`
859Searching memory bytes with `memchr`
860Performance differences between `str` and `mem` functions
861Basic power and square root: `pow` and `sqrt`
862Exponential and logarithmic functions: `exp`, `log`, `log10`
863Trigonometric functions in radians
864Rounding with `ceil`, `floor`, and `round`
865Truncation and remainder: `trunc` and `fmod`
866Absolute values for floats with `fabs`
867Handling `NAN` and `INFINITY` constants
868Allocating memory with `malloc` and `free`
869Contiguous allocation with `calloc`
870Resizing blocks with `realloc`
871Converting strings to integers with `atoi` and `atol`
872Robust string-to-number conversion with `strtol`
873Converting strings to doubles with `strtod`
874Communicating with the OS using `system`
875Cleaning up at exit with `atexit`
876The generic signature of `qsort`
877Writing an integer comparison function
878Writing a string comparison function for `qsort`
879Sorting structs by multiple fields
880Using `bsearch` on sorted arrays
881Handling the `void*` return of `bsearch`
882Common pitfalls in comparison function logic
883Generating pseudo-random numbers with `rand`
884The importance of the `RAND_MAX` constant
885Seeding the generator with `srand`
886Why you should only seed once
887Scaling `rand` results to a specific range
888Getting a unique seed with `time(NULL)`
889Getting system time with `time_t`
890Measuring intervals with `difftime`
891Breaking down time with `struct tm`
892Converting `time_t` to local time with `localtime`
893Converting `time_t` to UTC with `gmtime`
894Formatting time strings with `strftime`
895Converting `struct tm` back to `time_t` with `mktime`
896Measuring CPU ticks with `clock`
897The global `errno` variable
898Interpreting errors with `perror`
899Getting error strings with `strerror`
900Resetting `errno` before library calls
901Using `assert` for internal debugging
902Disabling assertions with `NDEBUG`
903When to use `errno` vs return codes
904Integer ranges in `limits.h`
905Using `INT_MAX` and `INT_MIN` for overflow checks
906Platform-specific character sizes
907Precision and epsilon in `float.h`
908Checking `FLT_DIG` and `DBL_DIG` for precision limits
909Managing large constants: `LONG_MAX` vs `LLONG_MAX`

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Lesson 893 of 1,219·12. The Standard LibraryPro lesson

Converting `time_t` to UTC with `gmtime`

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