MCU C language string operation

Function prototype int atoi(const char *nptr);
int val = atoi("12");
so va is equal to 12

int to string itoa
function prototype: char*itoa(intvalue,char*string,intradix);
int number=123456;
char string[25];
itoa(number,string,10);
string is 123456. The 10 at the end means it is converted to decimal. 16 means it is converted to hexadecimal. 8 means it is converted to octal. It can also be converted to binary.

String interception strncpy
prototype: char*strncpy(char*dest,char*src,size_tnum);
As we all know, strcpy is a sub-link to copy strings. You may not know that there is also strncpy, which copies a string of a specified length.
chardes[]="Hello,iam!";
charsource[]="abcdefg";
strncpy(chardes,charsource,3);
At this time, the value of chardes is abc Note that here, abc is not added after !. Instead, the value is assigned from the first address of the chardes array, and '\0' is added as the terminator.
Change the usage to
strncpy(chardes+1,charsource+2,3);
At this time, the value of chardes is Hcde. Why is it this value? Do you understand? Think about it yourself. Offset.

String construction sprintf
prototype int sprintf( char *buffer, const char *format, [ argument] … );
This should be known to many people.
char dest[20];
int val=12;
sprintf(dest,"val=%d",val);

The value of dest is "val=12". The 12 is also a string. Please note.
This function can also convert integer and floating point types to strings
sprintf(dest,"%f",3.1415926f);
dest is "3.1415926"

sprintf(dest,"The current time is %s, please note","2014-04-09 11:27:21"); The latter string can also be replaced by
the value of the variable dest, which is "The current time is 2014-04-09 11:27:21, please note"

Direct memory operation memset
prototype void *memset(void *s, int ch, size_t n);
char buffer[20];
strcpy(buffer,"1234567890");
memset(buffer,0,sizeof(char)*20);
At this time, the data in buffer is all 0

strcpy(buffer,"1234567890");
memset(buffer+2,6,sizeof(char)*2);
At this time, the buffer value is 1266567890.
This function can modify the memory of any data type. So if some data received from the serial port needs to be simply modified before being forwarded, this function can be used to modify it.

Let me introduce these first, and then I will add other things when I think of them
[2014-04-11 supplement]

The memcpy function is also good to use. It directly copies the byte array to the specified location, so I won’t talk about this.

String segmentation strtok
prototype char *strtok(char s[], const char *delim);
Decompose a string into a group of strings. s is the string to be decomposed, and delim is the delimiter string.

 
Output:
abc
d

Remember, you only need to specify a string when you split for the first time, and use NULL for subsequent splits. When p==NULL, it means the split is complete. Pointers are used here, and the pointer does not need to be released here.


Search string strstr
prototype char *strstr(const char *str1, const char *str2);
strstr() function searches for the first occurrence of a string in another string.
str1: target to be searched　
str2: object to be searched　

char str[]="1234 xyz";
char* str1=strstr(str,"34");
printf("%s",str1);
Display: 34 xyz

String comparison strcmp
prototype: extern int strcmp(const char *s1,const char * s2);
Compare s1 and s2. Return 0 if the two are equal. Return a non-zero value if they are not equal.

String concatenation strcat
prototype extern char *strcat(char *dest,char *src);
concatenate src to the end of dest value. Note that dest must have enough space to receive src, otherwise an error will occur.