8.2.3 Step 3: Locate the Code (Sun Studio 12: C User's Guide)

Sun Studio 12: C User's Guide

8.2.3 Step 3: Locate the Code

Now let’s return to the task we undertook at the beginning of this section: to identify the problem that is causing the error message out of storage to be printed. You have invoked cscope, the cross-reference table has been built. The cscope menu of tasks appears on the screen.

The cscope Menu of Tasks:

% cscope

cscope     Press the ? key for help


Find this C symbol:
Find this global definition:
Find functions called by this function:
Find functions calling this function:
Find this text string:
Change this text string:
Find this egrep pattern:
Find this file:
Find files #including this file:

Press the Return key to move the cursor down the screen (with wraparound at the bottom of the display), and ^p (Control-p) to move the cursor up; or use the up (ua) and down (da) arrow keys. You can manipulate the menu and perform other tasks with the following single-key commands:

Table 8–1 cscope Menu Manipulation Commands


Tab	Move to the next input field.
Return	Move to the next input field.
`^n`	Move to the next input field.
`^p`	Move to the previous input field.
`^y`	Search with the last text typed.
`^b`	Move to the previous input field and search pattern.
`^f`	Move to the next input field and search pattern.
`^c`	Toggle ignore/use letter case when searching. For example, a search for `FILE` matches `file` and `File` when ignoring the letter case.
`^r`	Rebuild cross-reference.
`!`	Start an interactive shell. Type `^d` to return to `cscope`.
`^l`	Redraw the screen.
`?`	Display the list of commands.
`^d`	Exit `cscope`.

If the first character of the text for which you are searching matches one of these commands, you can escape the command by entering a \ (backslash) before the character.

Now move the cursor to the fifth menu item, Find this text string, enter the text out of storage, and press the Return key.

cscope Function: Requesting a Search for a Text String:

$ cscope

cscope     Press the ? key for help


Find this C symbol
Find this global definition
Find functions called by this function
Find functions calling this function
Find this text string:  out of storage
Change this text string
Find this egrep pattern
Find this file
Find files #including this file

Note –

Follow the same procedure to perform any other task listed in the menu except the sixth, Change this text string. Because this task is slightly more complex than the others, there is a different procedure for performing it. For a description of how to change a text string, see 8.2.8 Examples.

cscope searches for the specified text, finds one line that contains it, and reports its finding.

cscope Function: Listing Lines Containing the Text String:

Text string: out of storage

  File Line
1 alloc.c 63 (void) fprintf(stderr, "\n%s:  out of storage\n", argv0);


Find this C symbol:
Find this global definition:
Find functions called by this function:
Find functions calling this function:
Find this text string:
Change this text string:
Find this egrep pattern:
Find this file:
Find files #including this file:

After cscope shows you the results of a successful search, you have several options. You may want to change one of the lines or examine the code surrounding it in the editor. Or, if cscope has found so many lines that a list of them does not fit on the screen at once, you may want to look at the next part of the list. The following table shows the commands available after cscope has found the specified text:

Table 8–2 Commands for Use After an Initial Search


`1` -`9`	Edit the file referenced by this line. The number you type corresponds to an item in the list of lines printed by `cscope`.
Space	Display the next set of matching lines.
`+`	Display the next set of matching lines.
`^v`	Display the next set of matching lines.
`—`	Display the previous set of matching lines.
`^e`	Edit the displayed files in order.
`>`	Append the list of lines being displayed to a file.
`\|`	Pipe all lines to a shell command.

Again, if the first character of the text for which you are searching matches one of these commands, you can escape the command by entering a backslash before the character.

Now examine the code around the newly found line. Enter 1 (the number of the line in the list). The editor is invoked with the file alloc.c with the cursor at the beginning of line 63 of alloc.c.

cscope Function: Examining a Line of Code:

{
   return(alloctest(realloc(p, (unsigned) size)));
}

/* check for memory allocation failure */

static char *
alloctest(p)
char *p;
{
    if (p == NULL) {
        (void) fprintf(stderr, "\n%s:  out of storage\n", argv0);
        exit(1);
    }
    return(p);
}
~
~
~
~
~
~
~
"alloc.c" 67 lines, 1283 characters

You can see that the error message is generated when the variable p is NULL. To determine how an argument passed to alloctest() could have been NULL, you must first identify the functions that call alloctest().

Exit the editor by using normal quit conventions. You are returned to the menu of tasks. Now type alloctest after the fourth item, Find functions calling this function.

cscope Function: Requesting a List of Functions That Call alloctest():

Text string: out of storage

  File Line
1 alloc.c 63(void)fprintf(stderr,"\n%s:  out of storage\n",argv0);


Find this C symbol:
Find this global definition:
Find functions called by this function:
Find functions calling this function:  alloctest
Find this text string:
Change this text string:
Find this egrep pattern:
Find this file:
Find files #including this file:

cscope finds and lists three such functions.

cscope Function: Listing Functions That Call alloctest():

Functions calling this function: alloctest
File Function Line
1 alloc.c mymalloc 33 return(alloctest(malloc((unsigned) size)));
2 alloc.c mycalloc 43 return(alloctest(calloc((unsigned) nelem, (unsigned) size)));
3 alloc.c myrealloc 53 return(alloctest(realloc(p, (unsigned) size)));


Find this C symbol:
Find this global definition:
Find functions called by this function:
Find functions calling this function:
Find this text string:
Change this text string:
Find this egrep pattern:
Find this file:
Find files #including this file:

Now you want to know which functions call mymalloc(). cscope finds ten such functions. It lists nine of them on the screen and instructs you to press the space bar to see the rest of the list.

cscope Function: Listing Functions That Call mymalloc():

Functions calling this function: mymalloc

File         Function       Line
1 alloc.c    stralloc       24 return(strcpy(mymalloc
                            (strlen(s) + 1), s));
2 crossref.c crossref       47 symbol = (struct symbol *)mymalloc
                            (msymbols * sizeof(struct symbol));
3 dir.c      makevpsrcdirs  63 srcdirs = (char **) mymalloc
                            (nsrcdirs * sizeof(char*));
4 dir.c      addincdir      167 incdirs = (char **)mymalloc
                            (sizeof(char *));
5 dir.c      addincdir      168 incnames = (char **)
                            mymalloc(sizeof(char *));
6 dir.c      addsrcfile     439 p = (struct listitem *) mymalloc
                            (sizeof(struct listitem));
7 display.c  dispinit       87 displine = (int *) mymalloc
                            (mdisprefs * sizeof(int));
8 history.c  addcmd         19  h = (struct cmd *) mymalloc
                            (sizeof(struct cmd));
9 main.c     main           212 s = mymalloc((unsigned )
                            (strlen(reffile) +strlen(home) + 2));

* 9 more lines - press the space bar to display more *
Find this C symbol:
Find this global definition:
Find functions called by this function:
Find functions calling this function:
Find this text string:
Change this text string:
Find this egrep pattern:
Find this file:
Find files #including this file:

Because you know that the error message out of storage is generated at the beginning of the program, you can guess that the problem may have occurred in the function dispinit() (display initialization).

To view dispinit(), the seventh function on the list, type 7.

cscope Function: Viewing dispinit() in the Editor:

void
dispinit()
{
        /* calculate the maximum displayed reference lines */
    lastdispline = FLDLINE -  4;
    mdisprefs = lastdispline -  REFLINE + 1;
    if (mdisprefs > 9) {
       mdisprefs = 9;
    }
       /* allocate the displayed line array */
   displine = (int *) mymalloc(mdisprefs * sizeof(int));
}
^L/* display a page of the references */

void
display()
{
    char file[PATHLEN + 1]; /* file name */
    char function[PATLEN + 1];/* function name */
    char linenum[NUMLEN + 1]; /* line number */
    int screenline; /* screen line number */
    int width; /* source line display width */
    register int i, j;
"display.c" 622 lines, 14326 characters

mymalloc() failed because it was called either with a very large number or a negative number. By examining the possible values of FLDLINE and REFLINE, you can see that there are situations in which the value of mdisprefs is negative, that is, in which you are trying to call mymalloc() with a negative number.