Dynamic Allocation, Arrays of Pointers

Software Engineering

Programming in C

Class Syllabus #8

Dynamic Allocation, Arrays of pointers

/*strArray.h*/

/*This module performs operations on an array of char* . Note that

it is the responsibility of the user to call initArray() before doing

anything else.

The convention that the array either contains a pointer to a string

or a NULL pointer.

In all functions, the set of parameters (char ** stringArray, int length)

means the pointer to the beginging of the char* array, and the length

of the char* array.*/

void initArray(char ** stringArray, int length);

//set All pointers in Array to NULL

//note that, this function may not be called after memory has

//been allocated

void clearArray(char ** stringArray, int length);

//clear all entries in the Array, (freeing memory)

int numInArray(char ** stringArray, int length);

//return the number of strings that the array points to

//(this is the number of non-NULL pointers)

void stringToArray(char ** stringArray, int position, char * sourceString);

//copy sourceString to the array, into the spot: position

//note that it is the user's responsiblity that position is valid

void removeElement(char ** stringArray, int position);

//removes the string in position, users responsibility that

//position is valid index

/*strArray.c*/

#include "strArray.h"

#include <stdlib.h>

#include <string.h> //for strlen()

void initArray(char ** strA, int len)

{

int i;

for(i=0; i<len; i++)

strA[i]=NULL; //note that if strA[i] had a pointer to memory

//than this memory is lost and a leak is created

}

void clearArray(char ** strA,int len)

{

int i;

for(i=0;i<len;i++)

{

free(strA[i]);

strA[i]=NULL;

}

}

int numInArray(char ** strA,int len)

{

int i;

int num=0;//the number of strings pointed to by the the array

for(i=0;i<len;i++)

num += (strA[i] != NULL) ;

return num;

}

void stringToArray(char ** strA, int pos, char * pc)

{

char * pdest;

free(strA[pos]);

//free array and allocate memory for new string + 1 for '\0'

pdest=strA[pos]=(char *) malloc( (strlen(pc) + 1) * sizeof(char) );

while( *pc ) //this loop is strcpy()

*(pdest++) = *(pc++);

*pdest='\0'; //seel off the string

}

void removeElement(char ** strA, int pos)

{

free(strA[pos]);

strA[pos]=NULL;

}

/*main.c*/

#include "strArray.h"

#include <stdio.h>

#define NUM_STRINGS 10

void main()

{

int i;

char * stringArray[NUM_STRINGS];

initArray(stringArray,NUM_STRINGS);

stringToArray(stringArray,0,"This is string in position zero");

stringToArray(stringArray,3,"This is string in position three");

stringToArray(stringArray,6,"This is string in position six");

stringToArray(stringArray,9,"This is string in position nine");

printf("Number of strings in array: %d\n",

numInArray(stringArray,NUM_STRINGS) );

printf("Now print the values of the array:\n");

for(i=0; i < NUM_STRINGS; i++)

printf("Element %d:%s\n",i,stringArray[i]);

}

OUTPUT:

Number of strings in array: 4

Now print the values of the array:

Element 0:This is string in position zero

Element 1:(null)

Element 2:(null)

Element 3:This is string in position three

Element 4:(null)

Element 5:(null)

Element 6:This is string in position six

Element 7:(null)

Element 8:(null)

Element 9:This is string in position nine

Additions and modifications to the above program:

1. Use a struct {char ** stringArray; int length;}; to allow the same functionality.

Introduce argv[], argc

Write a running statistics function using a static variable:

typedef enum {average, sum, mode} STAT_COMMAND;

float statistic(float * dataArray, int length, STAT_COMMAND com);

String functions from string.h, stdio.h, stdlib.h soted by category

int strlen(const char * string);
char * strcat(char * strDestination, const char * strSource);
char * strncat(char * strDest, const char * strSource, int count);
int strcmp(const char * string1, const char * string2);
int stricmp(const char * string1, const char * string2);
int strncmp(const char * string1, const char * string2, int count);
int strnicmp(const char * string1, const char * string2, int count);
char * strcpy(char * strDestination, const char * strSource);
char * strncpy(char * strDest, const char *strSource, int count);
char * strdup(const char * strSource);
char * strlwr(const char * string);
char * strupr(const char * string);
char * strset(const char * string, char c);
char * strnset(const char * string, char c, int count);
char * strchr(const char * string, char c);
char * strrchr(const char * string, char c);
int strspn(const char * string, const char * strCharSet);
int strcpsn(const char * string, const char * strCharSet);
char * strstr(const char * string, const char * strCharSet);
char * strtok(char * strToken, const char * strDelimit);
int sscanf(const char * buffer, const char * format [,argument] … ); <stdio.h>
long strtol(const char * nptr, char ** endptr, int base);
double strtod(const char * nptr, char ** endptr);
unsigned long strtoul(const char * nptr, char ** endptr, int base);
double atof(const char * str); <stdlib.h>
int atoi(const char * str); <stdlib.h>
long atol(const char * str); <stdlib.h>

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