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  • INTERVIEW QUESTIONS LANGUAGES C DETAILS
    Question :
    How can I call system when parameters (filenames, etc.) of the executed command arent known until run time
    Category C Interview Questions
    Rating (0.3) By 9 users
    Added on 11/17/2011
    Views 166
    Rate it!
    Answers:

    Just use sprintf (or perhaps strcpy and strcat) to build the command string in a buffer, then call system with that buffer. (Make sure the buffer is allocated with enough space;
    Here is a contrived example suggesting how you might build a data file, then sort it (assuming the existence of a sort utility, and Unix- or MS-DOS-style input/output redirection):
    char *datafile = "file.dat";
    char *sortedfile = "file.sort";
    char cmdbuf[50];
    FILE *fp = fopen(datafile, "w");

    /* ...write to fp to build data file... */

    fclose(fp);

    sprintf(cmdbuf, "sort < %s > %s", datafile, sortedfile);
    system(cmdbuf);

    fp = fopen(sortedfile, "r");
    /* ...now read sorted data from fp... */



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