How do I properly concatenate three strings and make a system call?

Question

C++ / C#

Good afternoon. There is this code in C:

char filenames[1000];
        memset(filenames, 0, 1000);
        printf("Enter filenames:\n");
        read(0, filenames, 1000);
        printf(filenames);
        char* part1 = "file ";
        char* part2 = "| grep 'C source' | wc -1";
        char* result = malloc(strlen(part1) + strlen(filenames) + strlen(part2) + 1);
        memset(result, 0, strlen(part1) + strlen(filenames) + strlen(part2) + 1);
        memcpy(result, part1, strlen(part1));
        memcpy(result, filenames, strlen(filenames));
        memcpy(result, part2, strlen(part2));
        printf(result);
        system(result);

The task is as follows: you need to get file names separated by spaces from the user. Next, I want to embed these names in the query "file | grep 'C source' | wc -1", and then make a call to this command using system. Unfortunately, it doesn't work for me. I tried to use strcat but it doesn't work either.

Answer 1

When doing memcpy, the pointer to result must be offset by the size of the previous copied line. Now you just copy the next line, overwriting the previous copy.

memcpy(result + strlen(part1), filenames, strlen(filenames));

strcat should work fine, it does essentially the same thing.
When copying strings, it's better to use strcpy (or strncpy), it copies with a terminating 0. memcpy is designed to copy memory of arbitrary content.