Incomplete statistics, C language there are as many as 15 in the standard library header files, so I mainly introduce the commonly used the four header files stdio. h, string. h, math. h, stdlib. h, after used the other to do added. The following dry goods:
1. < stdio.h > : defines input/output functions, types, and macros. Functions make up almost a third of the standard library.
(1) file access.
FILE *fopen (" filename "," mode ") :Open the file with the address ‘filename’ in mode mode and return the file pointer.
Access mode is mainly “r” : read only; “w” : write only and delete existing content; “a” : append, append at the end;
“r+”, “w+” : reading and writing; “a+” is appended, and “b” is added at the end above: base 2 file operation.
Note: where r is an open file, w is created (if the file does not exist); w overrides the original, and a appends to the end of the original file.
int fclose ( FILE *f ) :Release the buffer data and close the stream.
Here are two that I haven’t used much:
FILE *freopen (" filename "," mode ", FILE * f ) :Open the file with the address ‘filename’ in mode mode and associate it with the stream f2.
int fflush ( FILE *f ) :Writes to a file all data that has been written to a buffer but not to a file.
(2) base 2 input/output
fread ( *ptr . size . n . FILE* f ) :Read n objects of length size from f and put them into an array that ptr points to.
fwrite ( *ptr . size . n . FILE* f ) :Read n objects of length size from the ptr pointing array and write them to f.
Note: be aware of the write and read objects. Both reads and writes are for the f file stream.
(3) unformatted input/output
int fgetc/getc ( FILE *f ) :Returns the next character of the stream f, reaches the end of the file/error, returns EOF.
int fputc/putc ( int c . FILE *f )Enter the character c into the stream f.
int fgets ( char * s . int n . FILE *f ) :Read the next n-1 character in f into the array s. When a newline character is encountered, it terminates.
int fputs ( const char * s . FILE *f ) :Output the string s to the stream.
int fclose ( FILE *f ) :0
Write c back into f.
(4) format input/output
Output in 1 format.
scanf/fscanf/sscanf
printf/fprintf/sprintfNote: without f/s, it is the format string standard input/output function, input/output to terminal/screen; printf (const char *format…)
Add s, input/output to the string. sprintf (char *s, const char *format,…)
Add f, input/output to file stream. fprintf (FILE *f, const char *format,…)
(5) file location
long ftell ( FILE *f ) :Returns the current pointer position. Return -1L on error.
int fclose ( FILE *f ) :3
Set the current stream f pointer position to offset characters after origin. origin: SEEK_SET: file start location; SEEK_CUR pointer current location, SEEK_END: end of file location.
int fclose ( FILE *f ) :4
Pointer returns the starting position of the file, equivalent to: fseek (f, 0L, SEEK_SET)
Not commonly used:
int fclose ( FILE *f ) :5
Record the current position of the pointer to *p for use by the fsetpos function.
int fclose ( FILE *f ) :6
The pointer position points to *p.
(6) error handling and file operation
int feof ( FILE *f )Indicates the end of the file, with 1 returning 0 and a non-0 value at the end.
int ferror ( FILE *f )If the error indicator associated with f is set, a non-zero value is returned.
int fclose ( FILE *f ) :9
Deletes the file at the specified location.
int rename ( const char *oldname . const char *newname )Change the file name, otherwise return a non-zero value.
FILE *tmpfile ( void )Create a temporary file in ‘wb+’ mode and delete it automatically when it is closed or the program ends normally
2. < string.h > Divide into two groups, group 1 begins with str and group 1 begins with mem < memory.h > Not all compilers have them.)
(1) str
char * strcpy (char *dest, const char *src);Copy the string src to the string dest (including ‘\0’) and return dest
char * strncpy (char *dest, const char *src . n);Copy the former n characters from src into dest, return dest, and ‘\0’ will be added if there are not enough n characters.
char * strcat (char *dest, const char *src);
char * strncat (char *dest, const char *src . n);After connecting src to dest; The first n characters in src are connected to dest.
int strcmp (const char *s1, const char *s2);
int strncmp (const char *s1, const char *s2 . n); To compare s1 with s2 . s1<s2 Returns a negative number, otherwise 0 ; Compare the former n A character
char * strchr (const char *s, int c);
char * strrchr (const char *s, int c); Return string s In the first 1 Secondary occurrence character c Position pointer; Return string s In the last 1 Secondary occurrence character c Position pointer ( c Will be converted into a char )size_t strcspn (const char *s1, const char *s2); char * strdup (const char *s); char * strerror (int errnum);
(2) mem
void *memcpy ( void *s . const void *ct . n )Copy the first n characters from the string ct into s and return s.
void *memmove ( s . ct . n The above) 1 Function, but it still executes correctly when the objects overlap.
void *memset ( void *s . int c . n )Replace the first n characters in s with c and return s.
int memcmp ( cs . ct . n )n characters before cs are compared with ct, cs < ct, returns a negative number; Otherwise return 0
void *memchr ( cs . c . n )Returns a pointer to the first occurrence of c in cs.
3. < math.h > 1 some mathematical functions
Beg absolute value
int abs (int x);
long labs (long x);
float fabs ( float x ) :All return values are double, the Angle of the three-angle function is expressed in radians, x, y are all double
double acos (x);
double asin (x) ;
double atan (x);
double atan2 (y, x) : arctan ( y/x )
double tan (x);
double tanh (x) : Hyperbolic tangent
double sin (x);
double sinh (x);
double cos (x);
double cosh (x);
double pow (x, y) ; // Note that the return value is of type double precision
double sqrt (x);
double ceil (x) : Not less than x The minimum integer number of (round up)
double floor (x) : No greater than x Of the maximum integer type (rounded down)
double exp (x);
double fabs (x);
double log (x) : ln ( x )
double log10 (x);
double fmod (x, y) : x/y The remainder of
double ldexp (x, n) : x*2^n
double modf (x, double *ip): will x Divide into integer and decimal parts, return the decimal part, and put the integer part *ip In the
double frexp (x, int *exp); will x Divided into ( 0.5,1 ) between the 1 The sum of real fractions 1 a 2 Omega to the power of omega, which returns the true fraction, omega to the power of omega exp In the4. < stdlib.h > Numerical conversion, memory allocation and so on.
int rand ( void )Produces a random integer between 0 and 32767.
Pointer name = (data type *) calloc (n, size)
Allocate n contiguous Spaces of length size and set all elements to zero to return the first address.
Pointer name = (data type *) malloc (n*size)
Allocate n*size bytes of memory and return the first address.
Pointer name p1= (data type *) realloc (pointer name p2 to change memory size, new size n)
Allocate the space with the length of n bytes, assign the value of p2 to this memory, and return the first address to p1. (change the memory size of p1 to the address)
void free ( *p )Free the memory pointed by p (p is the memory allocated by malloc, realloc, calloc)
void abort ( void )Cause the program to terminate abnormally.
void exit ( int status )Cause the program to terminate normally.
conclusion