C Language--string

1. String

Representations: Char ch[5]={' A ', ' B ', ' C ', ' d ', ' e '};

Note the point:

Enclosed in double quotes.

Each character occupies a single byte

End of string as ' \ '

int main (int argc, const char * argv[]) {    char str[100]= "Hahahaha\0wewewe\0helloworld";    printf ("%s\n", str);    printf ("%s\n", &str[9]);    printf ("%s\n", &str[16]);    return 0;}

1.1 String length

Note the point:

String valid length does not contain '/'

sizeof is an operator that takes a variable or constant to take up the amount of memory space

Strlen is a function that asks for the number of valid characters in a string

int Mystrlen (const char * src) {    int i=0;    while (src[i]!= ') {        i++;    }    return i;} int main (int argc, const char *argv[]) {    char str[100]= "Hello World";    printf ("%d \ n", Mystrlen (str));//Call function to find the length    of printf ("%ld \ n", sizeof (str));    printf ("%ld \ n", sizeof ("Hello World"));    printf ("str = =%ld \ n", strlen (str));    return 0;}

1.2 string copy (copy)

Function:

strcpy

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

strncpy

Char *strncpy (char *, const char *, size_t);

Note the point:

S1 has enough memory space to hold S2 string

strncpy Select the number of bytes copied, does not necessarily include ';

Custom copy function char *mystrcpy (char *dst, const char *src) {    int i =0;    while (Src[i]) {        dst[i]=src[i];        i++;    }    dst[i]= ' + ';    return DST;} int main (int argc, const char *argv[]) {    char s1[100];    Char s2[50]= "Hello world\n";    Char *str = strcpy (s1, S2);    printf ("%s\n", strcpy (S1, S2));    printf ("%s\n", str);    printf ("%s\n", mystrcpy (S1, S2));    strncpy (S1, S2, ten);    s1[10]= ' + ';    printf ("%s\n", S1);        return 0;}

1.3 string concatenation

Function:

Strcat

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

Strncat:

Char *strncat (char *, const char *, size_t);

Strncat a new string after stitching will add a '/';

Custom stitching function Char *mystrcat (char *s1, const char *s2) {    int i=0,j;    while (S1[i]) {        i++;    }   Loop stitching operation for    (j=0; s2[j]!= '; j + +) {        s1[i+j]=s2[j];    }    s1[i+j]= ' + ';    return s1;} int main (int argc, const char *argv[]) {    char s1[100]= "Hello World";    Char s2[50]= "Wearefriend";        printf ("%s\n", strcat (S1, S2));    printf ("%s\n", Mystrcat (S1, S2));    printf ("%s\n", Strncat (S1, S2, 5));        return 0;}

1.4 String comparison function

Function:

strcmp

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

strncmp

int strncmp (const char *, const char *, size_t);

S1 > S2 Returns a positive number

S1 = = S2 return 0

S1 < S2 returns a negative number

Custom comparison function int mystrcmp (const char* s1, const char *s2) {    int i;    The loop is judged at the end of the string for    (i=0; (s1[i]!= ') && (s2[i]!= '); i++) {        if (S1[i]==s2[i]) {            continue;        }        Else        {break            ;            return  s1[i]-s2[i];        }    }    Returns a comparison number    return s1[i]-s2[i];} int main (int argc, const char *argv[]) {    char *str1 = "Borld";    Char *str2 = "Zorld";        printf ("%d\n", mystrcmp (STR1, str2));    printf ("%d\n", strncmp (str1, STR2, 7));    Char s1[30]= "Hello World";        return 0;}

1.5 String Lookup

Function:

STRCHR:

Char *STRCHR (const char *, int);

STRRCHR:

Char *STRRCHR (const char *, int);

Char *mystrchr (const char *S1, char ch) {    int i=0;    while (S1[i]) {        if (s1[i]==ch) {break            ;        }        i++;    }    Return (char *) &s1[i];} int main (int argc, const char *argv[]) {    char str[100]= "Hello world!";        Char *pstr = MYSTRCHR (str, ' l ');    printf ("%s\n", pstr);    printf ("%s\n", pstr);    return  0;}

1.6 Finding a string

Function:

Strstr

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

int main (int argc, const char *argv[]) {    char str1[100]= "HelloWorld HelloWorld";    printf ("%p\n", &str1[strlen (STR1))),//    char *pstr = strstr (str1, "World");//    printf ("%s\n", pstr)    ; char *p = str1;    while (P=strstr (p, "world")) {        if (p) {            printf ("%s\n", p);            P+=sizeof ("World")-1;        }    }    return 0;}

1.7 String Segmentation

Function:

Strtok

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

int main (int argc, const char *argv[]) {    char str[100]= "Hello World:good-bye:://we^are". Friend () ok///";//    char *p=strtok (str,": ");//    printf ("%s\n ", p);//While    ((P=strtok (NULL,":/^. () -"))) {//        printf ("%s\n ", p);/    }    char *p = str;    while (P=strtok (P, ":/^. () -")")    {        printf ("%s\n", p);        P=null;    }    p = strtok (NULL, ":");//    printf ("%s\n", p);    return 0;}

eg. dividing a string by a space to get the number of words (without using system functions)

int main (int argc, const char *argv[]) {    char str[200];    scanf ("%[^\n]", str);    int i=0;    int flag=1;//flag bit    int cnt=0;//statistic number while    (str[i]!= ') {if (        str[i]== ') {            if (!flag) {                flag = 1;
   }        }        else        {            if (flag) {                cnt++;                Flag =0;            }        }        i++;    }    printf ("%d\n", CNT);    return 0;}

C Language--string