wyuen@CAE.WISC.EDU (08/28/90)
Could someone give examples of how to use scandir?
Eg., how to list the filenames of a given directory?
It seems to me that
struct direct *(*namelist[]); is a reasonable declaration,
n = scandir(".", namelist, NULL, NULL) is a reasonable call,
for (i=0; i<n; i++)
printf("filename = %s\n", (*namelist[i])->d_name); is a reasonable use,
however, I'm getting Segmentation Faults all the time.
Someone kindly points out what I did wrong?
Thanks. Please send to newsgroup as my email is unstable.katsu@sra.co.jp (WATANABE Katsuhiro) (08/28/90)
# Sorry for my poor English. In article <9008271747.AA02292@ws-38.cae.wisc.edu> wyuen@CAE.WISC.EDU writes: > Could someone give examples of how to use scandir? > struct direct *(*namelist[]); is a reasonable declaration, > n = scandir(".", namelist, NULL, NULL) is a reasonable call, It's a `illegal pointer probrem'. The 2nd argument of scandir() must be the address in which you want scandir() to set the address of name list. Indeed TYPE of each identifiers are surely reasonable in your program. But `namelist' is uninitialized and it holds nonsense address and its VALUE is not reasonable. Anyway, my example: #include <sys/types.h> #include <sys/dir.h> main(argc, argv) int argc; char **argv; { int i, n; struct direct **namelist; if ((n = scandir(".", &namelist, NULL, NULL)) < 0) { perror(argv[0]); exit(1); } for (i = 0; i < n; i++) printf("filename = %s\n", namelist[i]->d_name); /* example of free-ing */ for (i = 0; i < n; i++) { free(namelist[i]->d_name); } free(namelist); exit(0); } ----____----____ WATANABE Katsuhiro Software Research Associates, Inc. Japan. Not execute, but evaluate.
gwyn@smoke.BRL.MIL (Doug Gwyn) (08/29/90)
In article <KATSU.90Aug28105457@sran14.sra.co.jp> katsu@sra.co.jp (WATANABE Katsuhiro) writes: >> n = scandir(".", namelist, NULL, NULL) is a reasonable call, No, it is not "reasonable". The only time you should pass uncast NULL arguments to a function is when there is a prototype for the function in scope, which is not possible in pre-ANSI C. In this particular case the last two arguments should be either (int(*)())NULL or (int(*)())0.
jmaynard@thesis1.hsch.utexas.edu (Jay Maynard) (08/29/90)
In article <KATSU.90Aug28105457@sran14.sra.co.jp> katsu@sra.co.jp (WATANABE Katsuhiro) thinks all the world's a VAX: >>> n = scandir(".", namelist, NULL, NULL) is a reasonable call, In article <13677@smoke.BRL.MIL> gwyn@smoke.BRL.MIL (Doug Gwyn) corrects him: >No, it is not "reasonable". The only time you should pass uncast NULL >arguments to a function is when there is a prototype for the function >in scope, which is not possible in pre-ANSI C. In this particular case >the last two arguments should be either (int(*)())NULL or (int(*)())0. This bears repeating. Sloppy programmers get away with cruft like this on benevolent architectures like the VAX, where everything is 32 bits and may be freely interchanged; when this is tried on other machines, though, it blows up because suddenly the wrong amount of stuff is added to or removed from the stack. If you're trying to write portable programs, please don't assume anything is interchangeable with anything else! -- Jay Maynard, EMT-P, K5ZC, PP-ASEL | Never ascribe to malice that which can jmaynard@thesis1.hsch.utexas.edu | adequately be explained by stupidity. "It's a hardware bug!" "It's a +--------------------------------------- software bug!" "It's two...two...two bugs in one!" - _Engineer's Rap_
george@hls0.hls.oz (George Turczynski) (08/31/90)
In article <9008271747.AA02292@ws-38.cae.wisc.edu>, wyuen@CAE.WISC.EDU writes: > > Could someone give examples of how to use scandir? > Eg., how to list the filenames of a given directory? > > It seems to me that > > struct direct *(*namelist[]); is a reasonable declaration, try: struct direct **namelist; > n = scandir(".", namelist, NULL, NULL) is a reasonable call, try: n= scandir(".",&namelist,NULL,NULL); > for (i=0; i<n; i++) > printf("filename = %s\n", (*namelist[i])->d_name); is a reasonable use, try: for( i= 0; i < n; i++ ) printf("filename= %s\n",namelist[i]->d_name); > however, I'm getting Segmentation Faults all the time. > Someone kindly points out what I did wrong? > > Thanks. Please send to newsgroup as my email is unstable. Perhaps you couldn't make sense of the manual entry ? I assume you _did_ read it, no ? You give it the address of a struct direct ** and it malloc()s the space for the pointer table and the structures, then "fills in" the struct direct ** ("namelist" here) with a pointer to the pointer table. You then use the pointer table to get to the struct directs. Here is the example you asked for: /*-----------------Cut here--------------------*/ #include<stdio.h> #include<sys/types.h> #include<sys/dir.h> struct direct **namelist; main() { int i, n; n= scandir(".",&namelist,NULL,NULL); for( i= 0; i < n; i++ ) printf("filename= %s\n",namelist[i]->d_name); } /*-----------------Cut here--------------------*/ Hope this clears up any problems, and have a nice day... -- | George P. J. Turczynski. |---------------------------------------------------- | Computer Systems Engineer. | ACSnet: george@highland.oz | I can't speak for the | | Highland Logic Pty. Ltd. | Phone: +61 48 683490 | company, I can barely | | Suite 1, 348-354 Argyle St | Fax: +61 48 683474 | speak for myself... | | Moss Vale. NSW. Australia. 2577 |----------------------------------------------------