Libc/stdio bug in Solaris!?

Question

Hello,
I was testing the following code using gcc + cc on Solaris 10 x86 & Solaris 8 sparc, both times it breaks. It breaks inside a call to fprintf. According to the man-pages I should not do a read after write without a flush/position change (which is done). I should not do a write after read without a position change or if the input reached the end of the file (which is the case here). So I assume that either I overlooked something or there is a subtle bug in the implementation stdio.
Greeting
Matthias Kretschmer
The "bad guy":
#include <stdlib.h>
#include <stdio.h>
int
main(int argc, char **argv)
FILE *fp;
int i, j, k;
int values[37];
char buf[256];
/* initialize values to bullshit */
for (i=0; i<37; i++)
values[i] = rand() % 32;
/* open file */
if ((fp = fopen("test.txt", "a+")) == NULL) {
perror("fopen");
exit(1);
/* loop to write and then read all */
for (j=0; j<100; j++) {
printf("j=%d\n", j);
/* loop for writing all */
for (i=0; i<10000; i++) {
for (k=0; k<37; k++)
if (fprintf(fp, " %d", values[k]) < 0) {
perror("fprintf");
exit(1);
if (fprintf(fp, "\n") < 0) {
perror("fprintf");
exit(1);
printf("write done\n");
/* seek to beginning */
if (fseek(fp, 0, SEEK_SET) < 0) {
perror("fseek");
exit(1);
printf("seek done\n");
/* read in everything */
while (fgets(buf, 256, fp) != NULL) ;
/* with the following code it doesn't crash for me on Solaris */
#if 0
if (fseek(fp, 0, SEEK_END) < 0) {
perror("fseek");
exit(1);
#endif
printf("read done\n");
}

Answer 1

Hello.
Please try if the "printf("seek done\n");" line has been reached by adding an "fflush(stdout);" after that line - otherwise you will not get the message if the program crashes. (If the program crashes the data written by successful fprintf()s will also be gone.)
Maybe the "fgets(buf, 256, fp)" is the problem because buf is 256 bytes long - but it must be 257 (258 ?) bytes long due to the trailing NUL byte.
Martin