CODEWITHSUNDEEP
cstringfor-loop
Mansueli
Mansueli

Reputation: 6939

For loop doesn't stop on the strlen

My biggest problem is on this line:

for(i=0;i<=strlen(enc);i++) ->

7th line of the function decifrar: It keeps the loop even with the memset used to clear the memory (it's even bigger than the string length)

Note if I use the actual length of the string in that line the code does works (i.e. replacing strlen(enc) with 60 )

void decipher(int k, char *enc){
     char alfa[]="9876543210zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA9876543210zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA";
     char *pch;
     int i;
     for(i=0;i<=strlen(enc);i++){
        pch=strchr(alfa, enc[i]);
        if (pch) enc[i] = *(pch + k),enc[i]=tolower(enc[i]);
     }
     printf("%s",enc);
}
int main(){
    int keys[6]={1,4,15,24,12,20},i;
    char *txt="rfgr r hz grkgb fvzcyrf dhr cergraqr fre grfgnqb ab cebtenzn";
    char *txttemp=malloc(sizeof(char)*1024);

    for(i=0;i<6;i++){
        printf("\n\n\t Attempt number: %d\n\n",i+1);
        memset(txttemp,'\0',sizeof(char)*strlen(txt)+30);
        memcpy(txttemp, txt, strlen(txt));
        decipher(keys[i],txttemp);
    }
    return 0;
}

What is the point that I am missing? Is the usage of strlen wrong?

Upvotes: 2

Views: 465

Answers (1)

Mene
Mene

Reputation: 3799

It's < not <= in the for-loop.

But as a Note: avoid that pattern. Strlen means you count the length of the string, but you probably should already know it from somewhere (i.e. when you receive it: the file length, the number of charecters returned etc...). Save it and take that value as the length. This is the source of a lot of security holes in programs (a buffer overflow).

std::string has this as a built-in functionality and it's what I would recommend over a plain char* almost all of the time (that is if you can use C++)

Upvotes: 7

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