strlen(a) → get the length of a
strncat(a,b,sizeOfA) → append b to a
strchr(a,'a') → search for first occurence of 'a' in string a
strrchr(a,'a') → search for last occurence of 'a' in string a
strstr(a,b) → search for string b in a
strncmp(a,b,sizeOfA) → compare strings a and b
strncpy(a,b,sizeOfA) → copy b to a (overwrite a)
memcmp(a,b,FirstNBytesToCompare) → compare first n bytes
memchr(a,'a',sizeOfA) → search array a for character 'a'
strtok(a,t) → tokenize string a by string t
or
or
https://en.cppreference.com/w/c/string/byte
#include <string.h>
the functions with an extra "n" in their names are safer to use because they check for size and can prevent errors or buffer overflow.
n is usually the length of first variable replace first variable content with second one
char src[20], dest[20]; → defines two empty strings
strcpy(src, "this is source"); → appends to strings
strcpy(dest, "this is destination");
strcat(s1,s2) / strncat(s1,s2,n) → combining two character strings together and puts the result in the first one: n is usually the length of first variable
strcat(first,second); → a copy of second string is appended to the first string and the result is saved to the first string, second one is not altered
printf("string: %s", (strncat(var1,var2,__size_t 100)));
char var1[]="A",var2[] = "B";
printf("cat: %s",strcat(var1,var2));
strcmp(s1,s2) / strncomp(s1,s2,n) → determing if two strings are equal n is usually the length of first variable this function does for string what relational operators do for numbers: if it returns 0, the strings are same and none-zero if it returns < 0 (negative value) then string1 is less than string2 if it returns > 0 (posetive value) then string2 is less than string1
the "less than" here means in alphabetic order for example:
printf("%d\n",strcmp("A","B")); → returns -1, A is less than B
printf("%d\n",strcmp("B","A")); → returns 1, B is greater than A
example:
#include <stdio.h>
#include <string.h>
int main(void)
{
char str[] = "ABCDEFG";
char *ps = memchr(str,'D',strlen(str));
if (ps != NULL)
printf ("search character found: %s\n", ps);
else
printf ("search character not found\n");
return 0;
}
Output:
search character found: DEFG
memcmp() → compare the first n bytes of two strings if equal, returns 0 if var1 > var2 returns positive if var2 > var1 returns negative n is the number of first bytes to compare.e.g: size_t 10
unsigned char var1[]="12345", var2[]="12346";
printf("%d",memcmp(var1,var2,__size_t n));
strchr() → searchs a given string for a specified character first arg is the string to be searched (the address of a char array) second arg is the character to search for the function will search the string starting at the beginning and return a pointer to the first position in the string where character is found. the address of this position in memory is of type char* described as the pointer to char.
to store the value that's returned you must create a variable that can store the address of a character.
char * ptr = strchr(a,'d');
if the character is not found the function returns a special value NULL. NULL is the equivalent of 0 for a pointer and represents a pointer that does not point to anything.
example:
const char str[] = "http://www.tutorialspoint.com";
const char ch = '.';
char *ret;
ret = strchr(str, ch);
printf("String after |%c| is - |%s|\n", ch, ret);
String after |.| is - |.tutorialspoint.com|
strstr() → the most usefull searching function, searchs one string for the first occurrence of a substring , returns a pointer to the position in the first string where the substring is found, if no match, returns NULL.
example:
char text[] = "evey dog has his day";
char word[] = "dog";
char *pFound = NULL;
pFound = strstr(text,word);
strtok() → function is used for tokenizing strings a token is a sequence of characters within a string that is bound by a delimiter. a delimiter can be anything, but should be unique to the string. spaces, commas, and periods are good examples.
breaking a sentence into words is called tokenizing
example:
char str[80] = "hello world - how are you - im w4lk3r";
const char s[2] = "-";
char *token;
token = strtok(str,s); // get the first token
while (token != NULL){
printf("%s\n",token);
token = strtok(NULL,s);
}
to extract all tokens:
int main() {
char string[50] = "Hello! We are learning about strtok";
// Extract the first token
char * token = strtok(string, " ");
// loop through the string to extract all other tokens
while( token != NULL ) {
printf( " %s\n", token ); //printing each token
token = strtok(NULL, " ");
}
return 0;
}
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example:
// copy any input as output
int main(){
int c;
c= getchar();
while (c != EOF){
putchar(c);
c=getchar();
example:
// count the number of lines
#include <stdio.h>
int main()
{
int c, ln = 0;
while((c = getchar()) != EOF){
if(c == '\n'){
++ln;
printf("number of lines: %d\n",ln);
}
}
return 0;
}
#include <stdio.h>
#include <string.h>
void reverse(char*, int, int);
int main()
{
char a[100];
gets(a);
reverse(a, 0, strlen(a)-1);
printf("%s\n", a);
return 0;
}
void reverse(char *x, int begin, int end)
{
char c;
if (begin >= end)
return;
c = *(x+begin);
*(x+begin) = *(x+end);
*(x+end) = c;
reverse(x, ++begin, --end);
}
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example:
#include <stdio.h>
#include <ctype.h>
int main(){
char a[100] = "hello world";
for (int i = 0; a[i] != '\0'; i++ ){
if(islower(a[i]))
printf("lower: %c\n",a[i]);
}
return 0;
}
#include <stdio.h>
#include <stdbool.h>
int main(){
char str[] = "Hello World";
int i;
char found_lower = false, found_upper = false;
for (int i = 0; str[i] != '\0'; i++) {
found_lower = found_lower || (str[i] >= 'a' && str[i] <= 'z');
found_upper = found_upper || (str[i] >= 'A' && str[i] <= 'Z');
if (found_lower && found_upper) break;
}
printf("%d",found_lower && found_upper);
return 0;
}