out range error

[hunterx893]

Hi guys, this is is my function that deciphers lines of code. The first step to decipher is to get rid of all the same chars like aaabbbyyyy ----> aby . The second step is to get rid of all the occurences of the substring of the first three characters of the string, an example would be l.pxyzl.ptol ---> xyztol

For some reason whenever i try to run the program and cout decrypt in the main this error comes up:
terminate called after throwing an instance of 'std::out_of_range'
what(): basic_string::erase
Aborted
I'm not sure how should I fix it. I know it is something wrong with what I erased with the erasing function but not sure how to fix it. I am a beginner in programming so please help me step by step :) .

So far this is my function:

string decrypt (string encrypted)
{

string decrypt,deleted;
int i, pos, n;



for (i=0; i < encrypted.length(); i++)
{
if((pos=decrypt.find(encrypted[i]))<0)
{
decrypt = decrypt + encrypted[i];
}

}

deleted = decrypt.substr(0,3);

decrypt.erase(0,3);

n=decrypt.find(deleted);

decrypt.erase(n,3);

while(decrypt.find(deleted) != decrypt.npos){

n=decrypt.find(deleted);
decrypt.erase(n,3);

}
return decrypt;
}

[kbw]

Have you tried stepping thru the code in a debugger, or tracing the function?

[hunterx893]

I did and it seems like the error is coming from here, but not sure why.

string decrypt (string encrypted)
{

string decrypt,deleted;
int i, pos, n;



for (i=0; i < encrypted.length(); i++)
{
if((pos=decrypt.find(encrypted[i]))<0)
{
decrypt = decrypt + encrypted[i];
}

}

deleted = decrypt.substr(0,3);

decrypt.erase(0,3);

n=decrypt.find(deleted);

decrypt.erase(n,3); <----------------------------------------------------- error probably because of this

while(decrypt.find(deleted) != decrypt.npos){

n=decrypt.find(deleted);
decrypt.erase(n,3);

}
return decrypt;
}

[wenqiwei]

assuming you passed l.pxyzl.ptol in, after you've gone through the first loop,

for (i=0; i < encrypted.length(); i++)
{
if((pos=decrypt.find(encrypted[i]))<0)
{
decrypt = decrypt + encrypted[i]; 
}

}

your function would've got rid of the second l.p in the string, so the string becomes: l.pxyztol. You then proceed to erase l.p, so the string becomes: xyztol.
Subsequent call to 'find' will return -1 since the substring isn't there anymore.

I don't think your first loop is doing what the spec is saying. If it was, then the second step in the spec is completely trivial.

[coder777]

decrypt.erase(n,3); <----------------------------------------------------- error probably because of this

Yes, because n will be -1 [string::npos] (you need to check that).

What you do is eliminating all second occurrence of a character no matter where. But I guess that you should eliminate all subsequent same characters?