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Editorial Team
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Asked: 2026-06-17T13:56:27+00:00

FILE *file = fopen(argv[1], r); if(file != NULL){ char command[MAX_BUFFER]; while(fgets(command, MAX_BUFFER, file) !=

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    FILE *file = fopen(argv[1], "r");
    if(file != NULL){
        char command[MAX_BUFFER];
        while(fgets(command, MAX_BUFFER, file) != NULL){ //read line
            //operations
        }
        fclose(file);
    }
    else write(fileno(stderr), ERROR_MESSAGE, strlen(ERROR_MESSAGE));

I’m working on a pretty basic UNIX shell implementation that reads and executes line by line from a file. From the above code, I’m trying to figure out why fclose() might fail since valgrind seems to be telling me that I’ve left this file descriptor open.

Am I correct in assuming that the “still reachable” 568 bytes in the leak summary refer to a failed fclose() somehow?

==25428== FILE DESCRIPTORS: 4 open at exit.
==25428== Open file descriptor 3: test
==25428==    at 0x4F186B0: __open_nocancel (syscall-template.S:82)
==25428==    by 0x4EAC628: _IO_file_fopen@@GLIBC_2.2.5 (fileops.c:233)
==25428==    by 0x4EA1265: __fopen_internal (iofopen.c:93)
==25428==    by 0x400C0C: main (in /home/Desktop/sh)
==25428== 
==25428== Open file descriptor 2: /dev/pts/0
==25428==    <inherited from parent>
==25428== 
==25428== Open file descriptor 1: /dev/pts/0
==25428==    <inherited from parent>
==25428== 
==25428== Open file descriptor 0: /dev/pts/0
==25428==    <inherited from parent>
==25428== 
==25428== LEAK SUMMARY:
==25428==    definitely lost: 0 bytes in 0 blocks
==25428==    indirectly lost: 0 bytes in 0 blocks
==25428==      possibly lost: 0 bytes in 0 blocks
==25428==    still reachable: 568 bytes in 1 blocks
==25428==         suppressed: 0 bytes in 0 blocks
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1 Answer

  1. Editorial Team

    Your visible code looks ok.
    But to answer your question: likely, but the problem is somewhere else 😉

    To debug your program, comment out ‘operations’, so you have an empty loop.
    Does valgrind still complain ?

    No: the problem very likely lies within the code you named ‘operations’.

    Remove the comments and compile with debugging symbols on (-g) and use valgrind with these options:
    valgrind –leak-check=yes –show-reachable=yes –track-origins=yes yourprogram

    Yes: (very unlikely) something else got smashed, try to valgrind with more commented code.

    To find bugs at compile time, use the compiler’s flags (e.g. gcc has -Wall -Wextra -Wwrite-strings -Wformat=2 -Wformat -Wformat-security -D_FORTIFY_SOURCE=2 and more).

    And make use of static analysers e.g. llvm/clang (compile with clang –analyze yourprogram.c)

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