C language some common string operations

1.

/*

Character

Char, stored in memory in ASCII;

operation function #include <ctype.h>

*/

int main (int argc, const char * argv[]) {    printf ("Isalnum (' a ') =%d\n", Isalnum (' a '));//isalnum (' a ') =1 judgment is a character    printf ("Isalpha (' a ') =%d\n", Isalpha (' a ')),//isalpha (' a ') =1 judgment is the English alphabet    printf ("IsDigit (' a ') =%d\n", IsDigit (' a ')) //isdigit (' a ') =0 judgment is the numeric character    printf ("Islower (' a ') =%d\n", Islower (' a '));//judgment is lowercase character    printf ("Isupper (' a ') =%d\n" , Isupper (' a '));//judgment is the uppercase character    printf ("Isxdigit (7) =%d\n", Isxdigit (7));//judgment is 16 binary number    printf ("ToLower (' a ') =%c\n" , ToLower (' a '));//turn into lowercase    printf ("ToUpper (' a ') =%c\n", ToUpper (' a '));//turn into uppercase letters    printf ("Digittoint (' a ') =%d\n ", Digittoint (' a '));//16 into 10-input    printf (" Ishexnumber (' a ') =%d\n ", Ishexnumber (' a '));//equivalent isxdigit judgment is 16 binary    printf ("Isnumber (' a ') =%d\n", Isnumber (' a '));//equivalent isdigit judgment is 10 binary numeric character      return 0;} <span style= "color: #e32400;" ></span>

2.

/*

manipulation functions for strings

1: basic input and output

printf ("%s", str); start with the STR address and print to the end of '

scanf ("%s", str); Starting with the address of str , the padding character ;// If the destination string is not large enough, it may go out of bounds ;

*/

int main () {    char str[100] = {' A ', ' a ', ' a ', ' a ', ' a '};    scanf ("%s", str);//he  will automatically add ' + ' after the input is finished;    printf ("%s\n", str);    for (int i=0;i<5;i++)    {        printf ("%c,ascii is%d\n", Str[i],str[i]);    }    return 0;}

3.

/*

Get ( receive address )// and scanf the same is to ' \ n ' cutoff , you can receive space ; but scanf can not receive space ;

Puts ( string header address )

Char *fgets (char * buff, int bufsize, FILE *); most read bufsize-1 characters

*/

int main () {    char str[100] = {' A ', ' a ', ' a ', ' a ', ' a '};//    gets (str);//Only one address can be run out of bounds; the runtime system will give an alarm; warning:this program uses gets (), which is unsafe.    Fgets (str, 5, stdin);//the security function, which means that only 5-1 characters are read from the buffer into STR;    Puts (str);    return 0;}

int main () {    char str[100]={};//1:buffer reasonably large; 2: First clear 0 is a good habit;    scanf ("%s", str);    printf ("%s\n", str);    return 0;    }

4.

/*

sprintf ( destination string , formatted string , parameter list ): Prints the formatted string to the destination string ;

sizeof () storage , the number of bytes occupied ; is an operator ;

strlen () function , strong correlation with content ; #include <string.h>

*/

int main () {    char str[100]={' A ', ' a ', ' a ', ' a '};//    printf ("Hello iOS%d\n", 1518);    sprintf (str, "Hello iOS%d\n", 1518);//convert arbitrary to string;    printf ("%s", str);}

5.

/*

Common handling functions for strings :

Find the character , return NULL if not found , find the return address ;

*/

#include <stdlib.h> #include <string.h>char *mystrchr (const char *s, char ch) {    char *p= (char *) s;    while (*p)    {        if (*p = = ch)        {            return p;        }        p++;    }    Return null;//not found, returns null pointer;} int main () {    char *p = "HelloWorld";    char *q;    Q = MYSTRCHR (P, ' l ');//character lookup, find the position of the character from inside the string, different from MEMCHR (), because MEMCHR is looking for 0 1;  The result is Lloworld    printf ("%s\n", q);    Q = STRRCHR (P, ' l ');//Reverse lookup character  result for LD    printf ("%s\n", q);    return 0;}

6.

/*

string comparison

int strcmp (const char *, const char *);

*/

int main () {    char *p1= "hello1";    Char *p2= "Hello0";    int rst;    rst = strcmp (P1, p2);    printf ("%d\n", rst);        rst = strncmp (P1, p2,3);//limit the comparison range;    printf ("%d\n", rst);    return 0;}

7.

/*

string copy ;

*/

int main () {    char str[100]={};    char *src = "Hello";//    strcpy (STR,SRC);//The destination buffer is large enough, otherwise it will cross;//    printf ("%s\n", str);        strncpy (str,src,sizeof (str)-1);//n=sizeof (DST)-1; In order to protect the destination buffer, it is necessary to reserve the Terminator; the copy is true length; mainly to limit the time to prevent cross-border    printf ("%s\n", str);    return 0;}

8.

/*

Find a string ;

Char *strstr (const char *, const char *);

*/

int main () {    char *str = "Helloqianfeng Isniubi";    Char *search = "Qianfeng";    char *p;    p = strstr (str,search);//is case-sensitive;    printf ("%s\n", p);    return 0;}

9.

/*

string concatenation function ;

*/

int main () {    char str[100]= "Hello";    Char *p = "ios1518";//    strcat (str, p);//append P string to str string to ensure that Str has sufficient space;//    printf ("%s\n", str);        Strncat (str, p, sizeof (str)-strlen (str)-1);//concatenation of the number of =sizeof (str)-strlen (str)-1, need to reserve a terminator;    printf ("%s\n", str);    return 0;}

10.

/*

string segmentation function ;

Char *strtok (char *, const char *);

*/

int main () {    char str[100]= "hello%>< (&* (World.qian>feng";    Char *demi = "%>< (&*.";    Char *p=str;//    p = strtok (str, demi);//    printf ("%s\n", p);//    P = strtok (NULL, Demi);//    printf ("%s\n", p );//    P = strtok (null, demi);//    printf ("%s\n", p);//    P = strtok (NULL, Demi);//    printf ("%s\n", p);//    p = strtok (NULL, Demi);//    printf ("%s\n", p);//split failed, return NULL, return end;/For    (int i=0;i<40;i++)//    {        printf ("Str[%d]=%c---ascii=%d", i,str[i],str[i]);//        printf ("\ n");/    } while    (P=strtok (P, Demi))    {        printf ("%s", p);        p = NULL;    }    return 0;}

11.

/*

extracting integers

*/

int main () {    char *p= " -1234.89";    int i;    I=atoi (p);    printf ("%d\n", i);//-1234        char *p2= "1234.56";    Double F;    F=atoi (p2);    printf ("%lf\n", f);//1234.000000    return 0;    }

12.

// Flip String

Char *reverse (char *s) {    int len = (int) strlen (s);    for (int i=0; I<strlen (s)/2; i++)    {        char sh = s[i];        S[i] = s[len-1-i];        S[len-1-i] = sh;    }    return s;} int main () {    char str[100]= "1234";    Reverse (str);    printf ("%s", str);//4321    return 0;}

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C language some common string operations