C结构值出现乱码

Question

Having the problem with the sender and receiver of the checksum . where I am using the struct to define the variables to be written into the pipe.

struct ANSWER
{
    int arr[BUFFER];
    int counter;
    int ans;
}a;         

The mechanism used for checksum is :

int chck(int value[],int count)
{
    int i,sum=0,checksum;
    for ( i=0; i<count; i++)
    {
        sum+=value[i];
    }
    printf("SUM IS :%d \n",sum);
    checksum=checksum^sum;
    printf("CHECKSUM IS : %d",checksum);
    return checksum;
}

The main problem is in writing in the pipe as

write(pipe,a,sizeof(a));

This writes all the contains using struct.

While at receiver side having problem in retrieving the specific values when I retrieve the values at receiver side I get garbled values in count and ans variables.

read(pipe,a,sizeof(a));
printf("COUNT : \n ",a.counter);

the values turn out to be garbled.

Main area:

void main(int argc, char * argv[])
{
    int pipe,i;

    pipe = open("devil",O_WRONLY);

    if ( pipe == -1 )
    {
        printf("ERROR NO PIPE FOUND \n");
    }

    printf("ENTER NUMBER OF ELEMENT : ");
    scanf("%d",a.counter);

    for ( i=0; i<a.counter; i++)
    {
        printf("ENTER NUMBER :");
        scanf("%d",&a.arr[i]);
    }

    a.ans=chck(a.arr,a.counter);

    printf("CHECKSUM IS : %d \n",a.ans);

    write(pipe,&a,sizeof(a));

}

Answer 1

Turning comment to answer, I suggest you add error checking to all your system and standard library calls (except printing to stdout/stderr, that's more clutter than it's worth for almost any app), something like:

int main(int argc, char * argv[])
{
    int pipe, i;

    pipe = open("devil",O_WRONLY);
    if ( pipe == -1 )
    {
        perror("open pipe");
        return EXIT_FAILURE;
    }

    printf("ENTER NUMBER OF ELEMENT : ");
    if (scanf("%d",&a.counter) != 1) 
    {
        fprintf(stderr, "scanf count IO or parse error, or EOF\n");
        return EXIT_FAILURE;
    }

    for ( i=0; i<a.counter; i++)
    {
        printf("ENTER NUMBER :");
        if (scanf("%d",&a.arr[i]) != 1)
        {
            fprintf(stderr, "scanf number IO or parse error, or EOF\n");
            return EXIT_FAILURE;
        }
    }

    a.ans=chck(a.arr,a.counter);
    printf("CHECKSUM IS : %d \n",a.ans);
    i = write(pipe,&a,sizeof(a));
    if (i == -1)
    {
        perror("write to pipe");
        return EXIT_FAILURE;
    }
    else if (i != sizeof(a))
    {
        fprintf(stderr, "write to pipe, partial write!\n");
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}

Notes: For pedantic code, write actually returns type ssize_t . I changed return type of main to int as that is required by standard. Please read manual page / docs of perror to understand what it does and how it prints the actual error message. EXIT_FAILURE and EXIT_SUCCESS are constants for the two standard-defined return values or exit codes, usually 1 and 0 respectively. And in a larger program, you would probably write helper functions or macros for error handling, and split the entire main function into multiple functions, to make the code look less cluttered.

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Additionally, you use checksum variable uninitialized in chck function. You should probably initialize it to 0, something like:

int chck(int value[],int count)
{
    int i = 0, sum = 0, checksum = 0;
    ....

In general, you should avoid having uninitialzied variables, it's too easy to forget when first using them, like demonstrated here... Also, turn on compiler warnings, so you will usually get a warning if you still do that accidentally.

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One more bug: your first scanf was missing & to get pointer to a.counter (required for scanf , to actually modify the original variable). A good compiler may also be smart enough to warn about passing suspicious arguments to scanf .