Parsing a string in C

Question

I want to parse a string and do some checks on the last character of the string. For example:

char *name = "angela";

int i;
for(i = 0; i <= strlen(name); i++) {
    if(name[i] == 'a' && i == strlen(name)) {
        *do something here*;
     }
}

I tried this but nothing happens. Why won't this work?

Not related to your problem, but you should call strlen() outside the loop and store its value in a variable. It's iterating over the entire string on each call. — Fred Larson
– Fred Larson, Commented Apr 23, 2013 at 20:08
store the value of strlen() instead of processing it every iteration. — Jonatan Goebel
– Jonatan Goebel, Commented Apr 23, 2013 at 20:09
Since name isn't volatile (and isn't getting modified in the loop), it's probable that the calls are all getting optimized down to a single call anyways. — Brian Knoblauch
– Brian Knoblauch, Commented Apr 23, 2013 at 20:22
@BrianKnoblauch: Perhaps. I don't know how good optimizers are determining loop invariants. — Fred Larson
– Fred Larson, Commented Apr 23, 2013 at 20:30

Paul R · Accepted Answer · 2013-04-23 20:16:48Z

10

Change:

for(i = 0; i <= strlen(name); i++) {
    if(name[i] == 'a' && i == strlen(name)) {

to:

for(i = 0; i < strlen(name); i++) {
    if(name[i] == 'a' && i == strlen(name) - 1) {

Reason: the first character in a C string, s, has index 0, and the last character has index strlen(s) - 1, for a total of strlen(s) characters.

edited Apr 23, 2013 at 20:16

answered Apr 23, 2013 at 20:05

Paul R

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1 Comment

Joker_vD Over a year ago

Also a fix for for: for(i = 0; i < strlen(name); i++)

michell90 · Accepted Answer · 2013-04-23 20:08:58Z

3

The function strlen returns the actual length of a string, not its last index. In your example "angela", strlen will return 6 but the last index of this character array is 5. So you have to use:

if(name[i] == 'a' && i == strlen(name) -1)

answered Apr 23, 2013 at 20:08

michell90

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Comments

Johnny Mnemonic · Accepted Answer · 2013-04-23 20:22:10Z

3

You can just check the last character of the string like this(no need to use a loop):

char *name = "angela";
if(strlen(name)>0)//do the check below only if the string is not empty
if(name[strlen(name)-1]=='a')
{
    //do something here
}

answered Apr 23, 2013 at 20:22

Johnny Mnemonic

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