Checking for Illegal characters in C++

ohmygoth · 12-06-2009, 10:09 PM

I'm trying to make a single program that ask for a string (to create a file later) and check if there is some illegal character, this is what I have, but I get "Segmentation fail", I'm using Gcc under linux

Quote:

int main()
{
string archivou;
cout << "Enter filename" << endl;
getline(cin,archivou);

char simbolos[]={};
strcpy(simbolos,archivou.c_str());
int i;
int erroree=0;
for (i=0;i<strlen(simbolos);i++){
if ((simbolos[i] < 47 && simbolos[i] > 57) || (simbolos[i] < 64 && simbolos [i] > 95) || (simbolos[i] < 97 && simbolos[i] > 122)){
erroree++;}
}
printf("%d errors",erroree);*/
}

What am I doing wrong?!

nadroj · 12-06-2009, 10:28 PM

I would think this is the problem

Code:

char simbolos[]={};
strcpy(simbolos,archivou.c_str());

Your allocating 'simbolos' 0 bytes of memory, then your putting stuff into it with strcpy (length of 'archivou.c_str()' bytes of memory). Two alternatives:

- change 'char simbolos[]={};' to 'char * simbolos', and dynamically allocate enough memory to it, based on the length of the 'archivou' string entered.

- or preferably: use the 'archivou' variable itself, theres no need for another variable (or array of variables such as char[]). You can use array syntax on strings, so just do the checks on the actual string, like

Code:

if ( archivou[i] < 47 //...

etc.

paulsm4 · 12-07-2009, 12:30 AM

Hi -

Nadroj is correct:

Code:

  // Wrong 
  char simbolos[]={};
  strcpy(simbolos,archivou.c_str());

  // Better
  int ilen = strlen (archivou.c_str());
  char *simbolos = new char[ilen + 1];
  strcpy(simbolos,archivou.c_str());

  // Best
  string simbolos  = new string(archivou);

However, as to your original question:

I'd strongly encourage you NOT to use hard-coded constants like "if ((simbolos[i] < 47 && simbolos[i] > 57)" and instead:

a) #include <ctype.h>
b) use the standard macros "isprint()", "isalpha ()", etc
(or the Unicode equivalents "iswprint()", etc)

IMHO .. PSM

smeezekitty · 12-07-2009, 12:36 AM

Quote:

char simbolos[]={};

HELLO! by default the compiler allocates 1 byte

Code:

char *simbolos = new char [2+strlen( archivou.c_str() )];

is ok.

ohmygoth · 01-13-2010, 01:29 PM

Tnx everybody, finally I used this code:

int RevisarExtension() {
int validos=0;
char key[] = "abcdefghijklmnñopqrstuvwxyzABCDEFGHIJKLMNÑOPQRSTUVWXYZ1234567890 -_.";
char * pch;
pch = strpbrk (archivo.c_str(), key);
while (pch != NULL) {
pch = strpbrk (pch+1,key); validos++;
}
}