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| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <stdio.h>
enum { BUFFERSIZE = 32 };
extern void initialize_data(char *data, size_t size);
void func(const char *file_name) {
char data[BUFFERSIZE];
char append_data[BUFFERSIZE];
FILE *file;
file = fopen(file_name, "a+");
if (file == NULL) {
/* Handle error */
}
initialize_data(append_data, BUFFERSIZE);
if (fwrite(append_data, BUFFERSIZE, 1, file) != BUFFERSIZE) {
/* Handle error */
}
if (fread(data, BUFFERSIZE, 1, file) != 0) {
/* Handle there not being data */
}
if (fclose(file); == EOF) {
/* Handle error */
}
} |
However, because the stream is not flushed between the call to fread() and fwrite(), the behavior is undefined.
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| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <stdio.h>
enum { BUFFERSIZE = 32 };
extern void initialize_data(char *data, size_t size);
void func(const char *file_name) {
char data[BUFFERSIZE];
char append_data[BUFFERSIZE];
FILE *file;
file = fopen(file_name, "a+");
if (file == NULL) {
/* Handle error */
}
initialize_data(append_data, BUFFERSIZE);
if (fwrite(append_data, BUFFERSIZE, 1, file) != BUFFERSIZE) {
/* Handle error */
}
if (fseek(file, 0L, SEEK_SET) != 0) {
/* Handle error */
}
if (fread(data, BUFFERSIZE, 1, file) != 0) {
/* Handle there not being data */
}
if (fclose(file); == EOF) {
/* Handle error */
}
} |
Risk Assessment
Alternately inputting and outputting from a stream without an intervening flush or positioning call is undefined behavior.
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