String from previous call "remembered" after next call to function

Question

I am having trouble with a project for a computer science class in c. I am calling a function I created that reads from a file, stores it in a char array, then sends this to another function I created so that I may print the result from a single line that contains a particular string called string. All seems to work except for one thing. If I want the whole document printed, I send in NULL in place of string. However, after this is done, the program also prints out the results of the last time the function was called without a NULL in place of string. I can't figure out why though. Any help is greatly appreciated. Here is the appropriate code.

/*getText.c*/
#include<stdio.h>
#include<errno.h>
#include<stdlib.h>
#include<string.h>    
#include"getText1.h"

void getFileText(char *fileName, char *keyWord)
{
        FILE *file = fopen(fileName, "r");
        char *answer = (char*)malloc(sizeof(char)*MAX_FILE);
        if(file != NULL)
         {
                fread(answer, sizeof(char), MAX_FILE, file);
                parseText(keyWord, answer);
        }
        else
        {
                perror("Error in getText.c, fopen:");
                exit(-1);
        }
        fclose(file);
        free(answer);
 }

void parseText(char *string, char *text)
{
    char buff[MAX_FILE];
    char * ptr;
    int a = 0;
       strcpy(buff, text);
       ptr = strtok(buff, "\n");
        if(string != NULL)
        {
               while(ptr != NULL && a == 0)
               {
                       if(strstr(ptr, string) != NULL)
                       {
                               printf("test1 ");
                               printf("%s\n", ptr);
                               printf(" test2\n");
                               a = 1;
                       } 
                        ptr = strtok(NULL, "\n");
               }
       }
       else
       {
               printf(text);
       }   
  }

/*main*/
#include<stdio.h>
#include<string.h>

#include"getText1.h"
#include"fileName.h"

int main ()
{
        getFileText("/proc/diskstats", "sda");
        printf("Uptime ");
        getFileText(UPTIME, NULL);
        getFileText(TIME, TIME_KEYWORD);
        printf("Kernel Version ");
        getFileText(KERNEL, NULL);
        return 0;    
}

And the problem I am getting is that the first call to getFileText() works fine, and prints out the appropriate line. However, when I call it again for UPTIME with string being NULL, it prints out the entire the /proc/uptime (or UPTIME) and then the entire /proc/diskstats and does the same thing when I call it for KERNEL, but it works frine when I call it for TIME.

Compile with all warnings and debug info (`gcc -Wall -g`). Learn to use the debugger (`gdb`) and perhaps [valgrind](http://valgrind.org/) — Basile Starynkevitch, Mar 09 '14 at 18:53

score 0 · Answer 1 · answered Mar 09 '14 at 18:55

In getFileText() you read from the file into the buffer you malloc'd, but you give no way of knowing where the end of the file was. Then in parseText you do strcpy(buff, text);. What's probably happening is that this is copying all of the file and then just copying dirty memory from after the end of where you read the file, which still contains contents from previous file reads.

The strcpy function reads until it finds a null byte, but you don't have any null byte at the end of where you read the file into. To fix this you will have to check the return value of fread to find out how many bytes were actually read, and then include in your program a method for the other functions to know where the end of the data is that they are supposed to be working with.

String from previous call "remembered" after next call to function

1 Answers1