deleting/editing file using "fwrite" garbage value left!!!

[deepmala8]

Hi,

I am also stuck with a problem in writing into the file .below explanation also helped me but my issue is yet not solved .I want to edit my file which looks like

IG_UDP_CPORTS="22,5060,5062"
TG_TCP_CPORTS="1,2,3"
EG_TCP_CPORTS="50,2"
IG_TCPP_CPORTS="60,62
IG_UDP_CPORTS="5060,5062"

I want to delete any value written in first line ( as m not able to edit any other line so i kept the line in first position to edit) say i want to delete 22 . After deletion my file first line looks like
IG_UDP_CPORTS="5060,5062"
2"

in next line there is some garbage value left

whole code is as follows,what i have done is i read first line from file and stored it in a string then did modifications in string and write modified string in file.

main(void)
{
    FILE * fp,* fw;
    char * line = NULL;
    size_t len = 0,len1=0,len2=0;
    char src[55],new_src[55];
    char port[6];
    int i,j,k,count=0,pos=0;

    fp = fopen("conf.apf", "r");
    if (fp == NULL)
        exit(EXIT_FAILURE);
    fgets(src,50,fp);
    len=strlen(src);

    printf("\nEnter port number to be replaced : \n");
    scanf("%s",port);
    len1=strlen(port);
    printf("%s and length of string %d\n", port,len1);
    strncpy(new_src,src,len);
    for (j=0; j<len1; j++)
        for(i=15; i<len; i++)
        {
            if (port[j]==src[i])
            {
                j++;
                printf("\nj=%d!!\n",j);
                if(j==len1)
                {
                    pos=i-len1;
                    printf("\nPort number matched !!\n");
                    break;
                }
            }
        }
    if (pos)
    {
        for(i=pos+1; i<len; i++)
            new_src[i]=src[i+len1+1];

        len2=strlen(new_src);
        printf("\nNow string is %s and length of string %d", new_src,len2);
        fw = fopen("conf.apf", "r+");
        if (fw == NULL)
            exit(EXIT_FAILURE);
        fwrite(new_src,len2 ,1 ,fw);
        printf( "\nport Removed successfully\n");
    }
    else
        printf("\nPort number NOT matched !!\n");
    fclose(fp);
    fclose(fw);
    exit(EXIT_SUCCESS);
}

[Ancient Dragon]

First, its not good to open the same file twice. Use just one FILE* pointer and use it for both reading and writing. Call fseek() to move the FILE pointer back to the beginning if you need to but its not necessary to open the file again.

The only way to delete parts of a file is to completely rewrite it. Read the entire file into memory, make whatever changes you want in memory, then write the whole thing back out again. If the file is too large to fit in memory all at the same time then you can to the same thing by reading and writing a single line at a time, but using two different files (the original for reading and another temp file for writing). I know that sounds like quite a hassle but, as you have already discovered, its the only way to successfully change the data in text files that have random length records.

[WaltP]

First, its not good to open the same file twice. Use just one FILE* pointer and use it for both reading and writing. Call fseek() to move the FILE pointer back to the beginning if you need to but its not necessary to open the file again.

I disagree. IMO it's better to open the file for read, close, then open for write. At least for beginners. But you should close the file before opening it a second time, and use the same FILE*.

The rest of AD's suggestion is right on.

[Ancient Dragon]

I disagree. IMO it's better to open the file for read, close, then open for write. At least for beginners. But you should close the file before opening it a second time, and use the same FILE*.

Either way will work ok, but leaving the first file open and opening it again can cause big problems.