String Functions COMP 1002/1402 Arrays of Strings char *pDays[7]; - - PDF document

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String Functions

COMP 1002/1402

Arrays of Strings

char *pDays[7]; pDays[0] ="Sunday"; pDays[1] ="Monday"; pDays[2] ="Tuesday"; pDays[3] ="Wednesday"; pDays[4] ="Thursday"; pDays[5] ="Friday"; pDays[6] ="Saturday";

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Pointers to Strings Walking thro’ Array

char **pWalker, **pLast ; pLast = &pDays[6] For (pWalker = pDays; pWalker <= pLast; pWalker++;) {Body of the Loop}

printf("%p -> %s\n", pWalker, *pWalker)

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Functions : gets and fgets

char *gets (char *strPtr); /*stdin */ char *fgets (char *strPtr, int size, FILE *fp);/* from file */

Fetches input string till '\n'

• If there is a problem it returns NULL
• Otherwise it returns the pointer
• gets Changes '\n' to '\0’; Not fgets

Functions gets and fgets

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Functions puts and fputs

int puts (const char *strPtr);/*to stdout */

• puts Changes '\0' to newline

int fputs (const char *strPtr, FILE

*fp);

/* outputs to file */

• fputs does not change '\0' to newline
• '\0' is dropped
• Outputs string may or may not have newline
• If there is a problem both return EOF

Functions : puts and fputs

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String Manipulation Functions

C has a variety of string functions

• Included in <string.h>
• All begin with str

Function : strlen (length)

Outputs : String Length (not including '\0') int strlen(const char *s); How to Use: char *pstr="Hello"; int i = strlen(pstr);

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Function : strlen (length)

char strng[81]; … fputs(strng, outFile); if (strng[strlen(strng) – 1] != '\n'){ fputs("\n", outFile); } /* If the last character in a “line” is not newline it inserts one….*/

String Copy (returns to)

char *strcpy(char *to, const char *from);

strcpy – Not safe, length not specified

char *strncpy(char *to, const char *from, int size);

strncpy – Safer because length is specified

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s t r c p y s t r n c p y

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String Compare

int strcmp(const char *str1,const char*str2);

strcmp – Length not specified

int strncmp(const char *str1,const char *str2, int size);

strncmp – Compare up to specified length

s t r c m p

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strncmp(str1,str2,size)

equal 3 "ABC123" "ABC" >0 str1 < str2 4 "ABC" "ABC123" equal 3 "ABC" "ABC123" <0 str1 < str2 4 "ABC456" "ABC123" equal 3 "ABC456" "ABC123" equal 8 "ABC123" "ABC123" Returns Results Size str2 str1

String Concatenate (returns to)

char *strcat(char *to, const char *from);

strcat – Not safe, length not specified

char *strncpy(char *to, const char *from, int size);

strncat – Safer because length is specified

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strcat & strncat Character in String

char *strchr(const char *string, char ch)

strchr – returns pointer to first match

char *strrchr(const char *string, char ch)

strrchr – returns pointer to last match

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strchr & strrchr String in String

char *strstr(const char *strng, const char *sub_str)

strstr – returns pointer to first match

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String Token

char *strtok(const char *strng, const char *delim)

strtok – returns pointer to first match after first delimiter If strng is NULL then returns next pointer

• NB. In the next slide the top string is wrong. There should only be a space

between SUM and =, and no the null character, ‘\0’.

s t r t

• k

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Scan Memory String

int sscanf(char *str, const char *format,…);

“Reads” memory into variables Uses format string of scanf... Returns number of variables read

sscanf

Allows more control over data from file

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Example : sscanf

Input: Einstein, Albert; 1234 67 D Code:

i = sscanf(strIn, "%25[^;]%*c%4s%d%*[^ABCDF]%c", name, stuNo, &score, &grade);

Format Memory String

int sprintf(char *str, const char *format,…);

“prints” variables into memory Uses format string of printf... Returns EOF if error occurs

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sprintf

Allows ease of use and control