c-string

https://www.tutorialspoint.com/cprogramming/c_strings.htm

functions for c string:

c++

// copy string s2 into s1
strcpy(s1, s2);

// concat s2 into end of s1
strcat(s1, s2);
    
// return length of string s1
strlen(s1);

// return 0 if s1 and s2 are the same, less than 0 if s1<s2, greater than 0 if s1>s2
strcmp(s1, s2);

// return a pointer to the first occurrence of charactor ch in string s1
strchr(s1, ch);

// return a pointer to the first occurrence of string s2 in string s1
strstr(s1, s2);

c-array

size of array

c++

int prices[5] = { 1, 2, 3, 4, 5 };

int size = sizeof prices / sizeof prices[0];

int size = sizeof prices / sizeof *prices;

printf("%u", size); /* 5 */

c-pointer

check if pointer is not null

c++

1 2	if(ptr) /* succeeds if p is not null / if(!ptr) / succeeds if p is null */

Operators for pointer

https://www.codingeek.com/tutorials/c-programming/operations-on-pointers-c-programming-language/

dangling pointer

A pointer initially holding valid address, but later the held address is released or freed. Then such a pointer is called as dangling pointer.

https://zh.wikipedia.org/wiki/%E8%BF%B7%E9%80%94%E6%8C%87%E9%92%88

c-diff between pointer, array, string

diff between array and pointer

https://stackoverflow.com/questions/30647709/differences-between-arrays-pointers-and-strings-in-c

https://stackoverflow.com/questions/1641957/is-an-array-name-a-pointer

https://blog.csdn.net/Hackbuteer1/article/details/6706562

array names in a C program are (in most cases) converted to pointers. One exception is when we use the sizeof operator on an array. If a was converted to a pointer in this context, sizeof a would give the size of a pointer and not of the actual array, which would be rather useless, so in that case a means the array itself.

c++

#include <stdio.h>
 
int main () {

   char name[] = "Zara Alsssssssssi";
   char *i = name;
   

   printf("Size of names = %d\n", sizeof(name));
   printf("Size of names = %d\n", sizeof(*i));

   return 0;
}

Code

1 2	Size of names = 18 Size of names = 1

diff between `char str and char str[]`

char *str = “abcd” 先在静态区为”hello”常量分配5Byte，接着在栈里为指针str分配4Byte（32位机器）并指向”abcd”字串的首地址，因此此时str是指向第一个字符‘a’的一个指针。

char str[ ] = “abcd” 在栈里分配连续的5Byte，内容为’a’,’b’,’c’,’d’,’\0’ 此时str是数组名，同时也可转化为指向数组第一个字符‘a’的指针常量。
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版权声明：本文为CSDN博主「CHENG Jian」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/gatieme/article/details/48716093

c-structure

structure declaration

struct tag_name {
   type member1;
   type member2;
   /* declare as many members as desired, but the entire structure size must be known to the compiler. */
};

struct tag_name my_structure; /* definition */

struct tag_name {
   type member1;
   type member2;
}my_structure1, my_structure2; /* directly define two struct variables */

typedef struct tag_name {
   type member1;
   type member2;
} struct_alias;

struct_alias  my_structure;

c-enum

https://www.geeksforgeeks.org/enumeration-enum-c/

c-bitfield

struct {
	type [member_name] : width ;
}

//example of a bit field variable which is able to hold a value up to 7
struct {
   unsigned int age : 3;
} Age;

c-input and output

standard input and output

https://www.tutorialspoint.com/cprogramming/c_input_output.htm

character: getchar, putchar

string: get, put, scanf, prinf

File I/O

https://www.tutorialspoint.com/cprogramming/c_file_io.htm

FILE *fopen( const char * filename, const char * mode );
int fclose( FILE *fp );  // returns zero if success
int fputc( int c, FILE *fp );
int fputs( const char *s, FILE *fp );
int fprinf(FILE *fp,const char *format,...) // same as fputs
int fgetc( FILE * fp ); // read a single character 
char *fgets( char *buf, int n, FILE *fp ); // read up to n-1 characters from the input stream referenced by fp, but it stops reading after encountering the first /n or end of file
int fscanf(FILE *fp, const char *format, ...) // read strings from a file, but it stops reading after encountering the first space character
    
size_t fread(void *ptr, size_t size_of_elements, size_t number_of_elements, FILE *a_file);
size_t fwrite(const void *ptr, size_t size_of_elements, size_t number_of_elements, FILE *a_file);