can't open file, file descriptor returns -1 value

Question

When I run this program. The file descriptor returns -1 value and hence the program terminates. I don't know why is this happening. As the pid value is exactly the name of the file that I want to open.

const char *psyn = "product/productId:";
char line[100];
pFile = fopen ("pids.txt" , "r");
 if (pFile == NULL) perror ("Error opening file");
else {
    while(fgets (line , sizeof(line) , pFile))
        {
        if (strstr(line, psyn) == line)
            {
            leng = strlen(line);
                    if( line[leng-1] == '\n' )
                        line[leng-1] = 0;
                    if( line[0] == '\n' )
                        line[0] = 0;
            pid = line+strlen(psyn)+1;
                            strcat(pid,t);

            leng = strlen(pid);
                    if( pid[leng-1] == '\n' )
                        pid[leng-1] = 0;

            fd = open(pid, O_RDWR, 0644);
              if (fd == -1)
                               cout<<"eror in file \n";
               else { //.. rest of the program}

Answer 1

pid = line+strlen(psyn)+1;

aroused my suspicions. First strlen() here is not efficient. Second the +1 is one longer than the string.

  
int opt_verbose;   // from -v option

    char psyn[] = "product/productId:"; // array, not pointer
    char line[100];
    FILE *pFile = fopen ("pids.txt" , "r");
     if (pFile == NULL) perror ("Error opening file");
    else {
        while(fgets (line , sizeof(line) , pFile))
        {
            char   *s = strstr(line, psyn);
            if ( s == line)
            {
                int leng;
                for ( leng = strlen(line);
                      leng > 0 && isspace(line[leng-1]);
                      leng-- )
                  line[leng-1] = '\0';

                char *pid = line + sizeof(psyn) - 1;    // sizeof without \0
                strcat(pid,t);
                leng = strlen(pid);
                if( pid[leng-1] == '\n' )
                    pid[leng-1] = 0;

                if ( opt_verbose )
                    printf( "VERBOSE: opening %s\n", pid );
                int fd = open(pid, O_RDWR, 0644);
                if (fd == -1)
                {     // perror is usually not sufficiently detailed
                    printf( "ERROR: open \"%s\" failed: (%d) %s\n",
                                        pid, errno, strerror(errno) );
                           // \"%s\" nicely shows unexpected spaces in paths.
                    continue;
                }