SSD6::内存处理不当分析例程

/*
 Author : stoneJam*/

//----------------------------------------------------------
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

/* return 1 if str is "1", 0 otherwise */
int checkIf1(char *str) {
        char *newstr = (char*)malloc(strlen(str) + 1);

  // ERROR #1
        // strcat(newstr, str); /* set newstr to str */
  // to set newstr to str we should use
  // strcpy(newstr, str);
  strcpy(newstr, str); /* set newstr to str */

        if (strcmp(newstr, "1") == 0) { /* newstr is "1" */
    //a memory leak occured here
    free(newstr);  // add this statement to free newstr before return
                return 1;
        }
        free(newstr);
        return 0;
}

void main() {
        char *strArr[4] = {"1", "2", "3", "4"};
        int i;
       
        for(i = 0; i < 4; i++) {
                printf("%d\n", checkIf1(strArr[i]));
        }
}

/*
 Author : stoneJam*/

//----------------------------------------------------------
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

struct data {
        char *str1, *str2;
};

/* returns two strings concatenated if they are not the same, NULL otherwise */
char *mergeSingleIfDifferent(char *s1, char *s2) {
        char *str = (char *) malloc(strlen(s1) + strlen(s2) + 1);
        if (strcmp(s1, s2) == 0) { /* strings are equal */
   // ERROR #2
   // if str is assigned to NULL
   // the memory malloc to it will never be freed
   // free str before set str to NULL
   free(str);
            str = NULL;    
        }
        else {
                strcpy(str, s1);
                strcat(str, s2);
        }
        return str;
}

/* copies merged strings (or NULL) into array of strings passed in (results) */
void mergeArrayIfDifferent(char *results[], char *strA1[], char *strA2[], int size) {
        int i;
       
        for(i = 0; i < size; i++) {
                results[i] = mergeSingleIfDifferent(strA1[i], strA2[i]);               
        }
}

void printAndFree(int c, char *str) {
        if (str != NULL) {
                printf("%d: %s\n", c, str);
                free(str);
        }
}

void main() {
        char *strArr1[8] = {"1", "2", "3", "4", "5", "6", "7", "8"};
        char *strArr2[8] = {"a", "2", "c", "4", "e", "6", "g", "8"};
        char *results[8];
        int i;
       
        mergeArrayIfDifferent(results, strArr1, strArr2, 8);
        for(i = 0; i < 8; i++) {
   // ERROR #1
            // printAndFree(i, results);
   // results's type is  char *[8]
   // while param2 of printAndFree is char*
   printAndFree(i, results[i]);
        }
}