Breaking Down Strings

[Toothkiller]

I am getting some errors I dont understand with this file. I'm trying to break down this string into pieces. I supposed to take the parts of the string that are within parentheses out and make them into a new string. It is supposed to do this until the string is empty.

|22|error: variable-sized object 'functions' may not be initialized|
|364|error: too many arguments to function 'void* malloc(size_t)'|
|50|error: at this point in file|

#include <iostream>
#include <math.h>
#include <strings.h>
#include <stdlib.h>
#include <cstdio>
#include <cstdlib>
using namespace std;

 string getstring (string question) {
    string mystring;
    cout << question;
    cin >> mystring;
    return mystring;
    }

int j,k,n;
string halftheproblem = "";

void breakdownfunction (string function) {
    string newfunction = "(" + function + ")";
    int functionlength = newfunction.size();
    char * functions[functionlength] = newfunction;
    int count = 0;
    for (int i=0; i<=functionlength; i++) {
        if (functions[i]=="(") {
            n = n+1;
        }
        if (functions[i]==")") {
            count = count + 1;
        }
        if (count != n) {
            break;
        }
    }

    do {
        for (int i=0; i<=functionlength; i++) {
            if (functions[i]=="(") {
                j=i;
            }
            if (functions[i]== ")") {
                k=i;
                break;
            }
        }
        for (int i=j; i<=k; i++) {
            string newstring = "";
            newstring = newstring + newfunction[i];
            string * pData;
            pData = (string*) malloc (i,sizeof(string));
            if (pData==NULL) exit (1);
        }
        for (int i=0; i<j; i++) {
            string newstring = "";
            newstring = newstring + newfunction[i];
            halftheproblem = newstring;
        }
        for (int i=k+1; i<=functionlength; i++) {
            string newstring = "";
            newstring = newstring + newfunction [i];
            newfunction = halftheproblem + newstring;
        }
    }
    while(newfunction != "");
    for (int i=0; i<n; i++) {
        cout << pData[n];
    }
}


int main()
{
    string question ="gimme function: ";
    string function = getstring(question);
    breakdownfunction(function);
}

[sohguanh]

string newfunction = "(" + function + ")";
int functionlength = newfunction.size();
char * functions[functionlength] = newfunction;

You are assigning a variable newfunction of C++ string datatype to an array of char * which may mean only the first element in the array functions is initialized. The rest maybe undefined.

pData = (string*) malloc (i,sizeof(string));

The C function malloc do not take 2 arguments as said by the warning void* malloc(size_t) which indicate only 1 argument.

[Galik]

I made a few notes in your code. I am confused by pData. I am not sure what it is meant to be/do.

#include <iostream>
#include <math.h>
#include <strings.h>
#include <stdlib.h>
#include <cstdio>
#include <cstdlib>
using namespace std;

 string getstring (string question) {
    string mystring;
    cout << question;
    cin >> mystring;
    return mystring;
    }

int j,k,n;
string halftheproblem = "";

void breakdownfunction (string function) {
    string newfunction = "(" + function + ")";
    int functionlength = newfunction.size();

    // Don't bother with char* just use string
    // char * functions[functionlength] = newfunction;
    int count = 0;
    for (int i=0; i<=functionlength; i++) {
        if (newfunction[i]=='(') { // note single quotes ' not "
            n = n+1;
        }
        if (newfunction[i]==')') { // note single quotes ' not "
            count = count + 1;
        }
        if (count != n) {
            break;
        }
    }

    do {
        for (int i=0; i<=functionlength; i++) {
            if (newfunction[i]=='(') {
                j=i;
            }
            if (newfunction[i]== ')') {
                k=i;
                break;
            }
        }
        for (int i=j; i<=k; i++) {
            string newstring = "";
            newstring = newstring + newfunction[i];

            // What is pData supposed to do?
            string * pData;
//            pData = (string*) malloc (i,sizeof(string));

            if (pData==NULL) exit (1);
        }
        for (int i=0; i<j; i++) {
            string newstring = "";
            newstring = newstring + newfunction[i];
            halftheproblem = newstring;
        }
        for (int i=k+1; i<=functionlength; i++) {
            string newstring = "";
            newstring = newstring + newfunction [i];
            newfunction = halftheproblem + newstring;
        }
    }
    while(newfunction != "");
    for (int i=0; i<n; i++) {
       // cout << pData[n]; // what is pData supposed to be?
    }
}


int main()
{
    string question ="gimme function: ";
    string function = getstring(question);
    breakdownfunction(function);
}

[sohguanh]

I am confused by pData. I am not sure what it is meant to be/do.

Good question I am also confused. Is this code written by you or by others ? It just malloc and then never assign values to it. Maybe someone can understand the original author intention ?

[Disch]

Also note that you should NEVER allocate complex types like string with malloc _{(unless you use placement new later)} as malloc does not call the constructor.

Using string without having its constructor called would have disasterous results.

[Toothkiller]

Yea, I see where I didnt assign Pdata, its supposed to pick up the newstring above it.

[Galik]

I think you should just make it an ordinary string. And you need to declare it OUTSIDE the loop otherwise it will be destroyed when the loop exits:

std::string pData;
do
{
    // ... stuff

    pData = newstring;

    // ... stuff
} while(newfunction != "")

    for (int i=0; i<n; i++) {
        cout << pData[n];
    }