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#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#define WRITE_NO 1024
int main() {
size_t size;
char *buf;
FILE *fp = open_memstream(&buf, &size);
assert(fp);
char c = 'A';
for (size_t i = 0; i < WRITE_NO; i++)
assert(fwrite(&c, sizeof(char), 1, fp) == 1);
// Flush the file to update the pointers.
assert(!fflush(fp));
assert(size == WRITE_NO);
for (size_t i = 0; i < size; i++)
assert(buf[i] == c);
// Check if the stream maintains a null-bye at the end.
assert(buf[size] == '\0');
// Stream should be expanded, size should be == 2*WRITE_NO.
assert(!fseek(fp, WRITE_NO, SEEK_END));
assert(!fflush(fp));
assert(size == 2*WRITE_NO);
assert(buf[size] == '\0');
// Check if it's filled with zero's.
for (size_t i = WRITE_NO; i < size; i++)
assert(buf[i] == '\0');
// Go back and overwrite the 0's with 'B'.
assert(!fseek(fp, -WRITE_NO, SEEK_CUR));
c = 'B';
for (size_t i = 0; i < WRITE_NO; i++)
assert(fwrite(&c, sizeof(char), 1, fp) == 1);
// Check if that happened.
assert(size == 2*WRITE_NO);
for (size_t i = WRITE_NO; i < size; i++)
assert(buf[i] == c);
assert(buf[size] == '\0');
// Go to the front and write 'B'.
assert(!fseek(fp, 0, SEEK_SET));
for (size_t i = 0; i < WRITE_NO; i++)
assert(fwrite(&c, sizeof(char), 1, fp) == 1);
// Check if that happened.
assert(size == 2*WRITE_NO);
for (size_t i = 0; i < size; i++)
assert(buf[i] == c);
assert(buf[size] == '\0');
// Close the file, we have tested everything.
assert(!fclose(fp));
free(buf);
return 0;
}
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