CWE Rule 672

This issue occurs when a function attempts to close a stream that was closed earlier in your code and not reopened later.

The standard states that the value of a FILE* pointer is indeterminate after you close the stream associated with it. Performing the close operation on the FILE* pointer again can cause unwanted behavior.

Remove the redundant close operation.

#include <stdio.h>

void func(char* data) {
    FILE* fp = fopen("file.txt", "w");
    if(fp!=NULL) {
        if(data)
            fputc(*data,fp);
        else
            fclose(fp);
    }
    fclose(fp); //Noncompliant
}

In this example, if fp is not NULL and data is NULL, the fclose operation occurs on fp twice in succession.

One possible correction is to remove the last fclose operation. To avoid a resource leak, you must also place an fclose operation in the if(data) block.

#include <stdio.h>

void func(char* data) {
    FILE* fp = fopen("file.txt", "w");
    if(fp!=NULL) {
        if(data) {
            fputc(*data,fp);
            fclose(fp);
        }
        else
            fclose(fp);
    }
}

This issue occurs when a function operates on a stream that you closed earlier in your code.

The standard states that the value of a FILE* pointer is indeterminate after you close the stream associated with it. Operations using the FILE* pointer can produce unintended results.

One possible fix is to close the stream only at the end of operations. Another fix is to reopen the stream before using it again.

#include <stdio.h>

void func(void) {
    FILE *fp;
    void *ptr;

    fp = fopen("tmp","w");
    if(fp != NULL) {
        fclose(fp);
        fprintf(fp,"text"); //Noncompliant
    }
}

In this example, fclose closes the stream associated with fp. When you use fprintf on fp after fclose, the Use of previously closed resource defect appears.

One possible correction is to reverse the order of the fprintf and fclose operations.

#include <stdio.h>

void func(void) {
    FILE *fp;
    void *ptr;

    fp = fopen("tmp","w");
    if(fp != NULL) {
        fprintf(fp,"text");
        fclose(fp);
    }
}