I have a memory mapped file, from which I wish to parse the contents of the buffer. The mmap() returns success, and I can print out the buffer contents to a file using fprintf successfully. However, when I try to access the buffer as an array in my program directly, I get a segmentation fault. Why is this happening? Here is the code:
#define PTT_DUMP "/home/dhruv/somefile"
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int fd_ptt_dump = open(PTT_DUMP, O_RDONLY);
struct stat struct_ptt_dump;
fstat(fd_ptt_dump, &struct_ptt_dump);
printf("\n\n\t\t\t --- The size of the dump is = %d -----\n\n", struct_ptt_dump.st_size);
char *membuffer;
char pid_num[100];
char cycles[100], instr[100], cpi[100] ;
int pid_index =0;
int cycles_index = 0;
int instr_index = 0;
int cpi_index = 0 ;
int len = (int)struct_ptt_dump.st_size;
int newline_count = 0;
int n = 0;
if( (membuffer = mmap(0, struct_ptt_dump.st_size, PROT_READ, MAP_FILE | MAP_PRIVATE, fd_ptt_dump, 0)) == (caddr_t) -1)
err_sys("mmap error");
/* If the following is uncommented, it prints fine */
/*
for ( n =0; n < struct_ptt_dump.st_size ; n++)
fprintf(fp_logfile,"%c", membuffer[n]);
*/
/* But, I really want to access the buffer as an array for speed if possible */
/* Here is where everything goes haywire */
while (newline_count != 5)
if ( membuffer[n++] == '\n' )
newline_count++ ;
/* printf returns OK, and I am able to skip newlines */
printf("\n\n newlines = %d\n\n 10 buffer characters", newline_count);
int k =0;
/* All code from here gives segmentation fault */
while ( membuffer[n++] != ' ' )
pid_num[pid_index++] = membuffer[n] ;
/* Even if I comment out everything from here on, the above assignment itself results in a segmentation fault */
pid_num[pid_index] = '\0';
printf("\n\n pid = %s", pid_num);
while ( membuffer[len--] != ' ' )
if ( membuffer[len] != '\n' )
cpi[cpi_index++] = membuffer[len];
cpi[cpi_index] = '\0';
for( ; membuffer[len] == ' ' ; len-- )
;
for(n=0; membuffer[len-n] != ' '; n++)
instr[instr_index++] = membuffer[len-n] ;
instr[instr_index] = '\0' ;
n++;
for( ; membuffer[len-n] != ' ' ; n++)
cycles[cycles_index++] = membuffer[len-n];
cycles[cycles_index] = '\0';
printf("\n\n\t\t\t\t ********** buffer values *************\n\n");
printf("\t\t\t\tdominant pid = %s\t cycles = %s\t instructions = %s\t cpi = %s \n\n", pid_num, cycles, instr, cpi);
fflush(STDOUT_FILENO);