String Functions

String Functions

Date: November 3, 2018
Author: Paul Lewallen
Category:
find()Description:
find(item) returns index of first item occurrence, else returns string::npos (a constant defined in the string library). Item may be char, string variable, string literal (or char array).

find(item, indx) starts at index indx.

Ex.
// userText is "Help me!"
userText.find('p') // Returns 3
userText.find('e') // Returns 1 (first occurrence of e only)
userText.find('z') // Returns string::npos
userText.find("me") // Returns 5
userText.find('e', 2) // Returns 6 (starts at index 2)
substr()Description:
substr(index, len) returns substring starting at index and having len characters.

Ex.
// userText is "http://google.com"
userText.substr(0, 7) // Returns "http://"
userText.substr(13, 4) // Returns ".com"
userText.substr(userText.length() - 4, 4) // Last 4: ".com"
push_back()Description:
push_back(c) appends character c to the end of a string.

Ex.
// userText is "Hello"
userText.push_back('?'); // Now "Hello?"
userText.length(); // Returns 6
insert()Description:
insert(indx, subStr) Inserts string subStr starting at index indx.

Ex.
// userText is "Goodbye"
userText.insert(0, "Well "); // Now "Well Goodbye"

// userText is "Goodbye"
userText.insert(4, "---"); // Now "Good---bye"
replace()Description:
replace(indx, num, subStr) replaces characters at indices indx to indx+num-1 with a copy of subStr.

Ex.
// userText is "You have many gifts"
userText.replace(9, 4, "a plethora of");
// Now "You have a plethora of gifts"
str1 + str2 Description:
Returns a new string that is a copy of str1 with str2 appended.

If one of str1, str2 is a string, the other may be a character (or character array).

Ex.
// userText is "A B"
myString = userText + " C D";
// myString is "A B C D"
myString = myString + '!';
// myString now "A B C D!"
myString = myString + userText;
// myString now "A B C D!A B"

Some C string modification functions.
Given:
char orgName[100] = “United Nations”;
char userText[20] = “UNICEF”;
char targetText[10];

strcpy()Description:
strcpy(destStr, sourceStr)

Copies sourceStr (up to and including null character) to destStr.

Ex.
strcpy(targetText, userText); // Copies "UNICEF" + null char
// to targetText
strcpy(targetText, orgName); // Error: "United Nations"
// has > 10 chars
targetText = orgName; // Error: Strings can't be
// copied this way
strncpy()Description:
strncpy(destStr, sourceStr, numChars)

Copies up to numChars characters.

Ex.
strncpy(orgName, userText, 6); // orgName is "UNICEF Nations"
strcat()Description:
strcat(destStr, sourceStr)

Copies sourceStr (up to and including null character) to end of destStr (starting at destStr's null character).

Ex.
strcat(orgName, userText); // orgName is "United NationsUNICEF"
strncat()Description:
strncat(destStr, sourceStr, numChars)

Copies up to numChars characters to destStr's end, then appends null character.

Ex.
strcpy(targetText, "abc"); // targetText is "abc"
strncat(targetText, "123456789", 3); // targetText is "abc123"

Some C string information functions.
Given:
char orgName[100] = “United Nations”;
char userText[20] = “UNICEF”;
char targetText[10];

strchr()Description:
strchr(sourceStr, searchChar)

Returns NULL if searchChar does not exist in sourceStr. (Else, returns address of first occurrence, discussed elsewhere).
NULL is defined in the cstring library.

Ex.
if (strchr(orgName, 'U') != NULL) { // 'U' exists in orgName?
... // 'U' exists in "United Nations", branch taken
}
if (strchr(orgName, 'u') != NULL) { // 'u' exists in orgName?
... // 'u' doesn't exist (case matters), branch not taken
}
strlen()Description:
size_t strlen(sourceStr)

Returns number of characters in sourceStr up to, but not including, first null character. size_t is integer type.

Ex.
x = strlen(orgName); // Assigns 14 to x
x = strlen(userText); // Assigns 6 to x
x = strlen(targetText); // Error: targetText may lack null char
strcmp()Description:
int strcmp(str1, str2)

Returns 0 if str1 and str2 are equal, non-zero if they differ.

Ex.
if (strcmp(orgName, "United Nations") == 0) {
... // Equal, branch taken
}
if (strcmp(orgName, userText) == 0) {
... // Not equal, branch not taken
}