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C User's Guide

Chapter 9

cscope: Interactively Examining a C Program

cscope is an interactive program that locates specified elements of code in C, lex, or yacc source files. With cscope, you can search and edit your source files more efficiently than you could with a typical editor. That's because cscope supports function calls--when a function is being called, when it is doing the calling--as well as C language identifiers and keywords.

This chapter is a tutorial on the cscope browser provided with this release and is organized into the following sections:

• The cscope Process
• Basic Use
• Unknown Terminal Type Error

The cscope Process

When cscope is called for a set of C, lex, or yacc source files, it builds a symbol cross-reference table for the functions, function calls, macros, variables, and preprocessor symbols in those files. You can then query that table about the locations of symbols you specify. First, it presents a menu and asks you to choose the type of search you would like to have performed. You may, for instance, want cscope to find all the functions that call a specified function.

When cscope has completed this search, it prints a list. Each list entry contains the name of the file, the number of the line, and the text of the line in which cscope has found the specified code. In our case, the list also includes the names of the functions that call the specified function. You now have the option of requesting another search or examining one of the listed lines with the editor. If you choose the latter, cscope invokes the editor for the file in which the line appears, with the cursor on that line. You can now view the code in context and, if you wish, edit the file as any other file. You can then return to the menu from the editor to request a new search.

Because the procedure you follow depends on the task at hand, there is no single set of instructions for using cscope. For an extended example of its use, review the cscope session described in the next section. It shows how you can locate a bug in a program without learning all the code.

Basic Use

Suppose you are given responsibility for maintaining the program prog. You are told that an error message, out of storage, sometimes appears just as the program starts up. Now you want to use cscope to locate the parts of the code that are generating the message. Here is how you do it.

Step 1: Set Up the Environment

cscope is a screen-oriented tool that can only be used on terminals listed in the Terminal Information Utilities (terminfo) database. Be sure you have set the TERM environment variable to your terminal type so that cscope can verify that it is listed in the terminfo database. If you have not done so, assign a value to TERM and export it to the shell as follows:

In a Bourne shell, type:

$ TERM=term_name; export TERM

In a C shell, type:

% setenv TERM term_name

You may now want to assign a value to the EDITOR environment variable. By default, cscope invokes the vi editor. (The examples in this chapter illustrate vi usage.) If you prefer not to use vi, set the EDITOR environment variable to the editor of your choice and export EDITOR, as follows:

In a Bourne shell, type:

$ EDITOR=emacs; export EDITOR

In a C shell, type:

% setenv EDITOR emacs

You may have to write an interface between cscope and your editor. For details, see Command-Line Syntax for Editors.

If you want to use cscope only for browsing (without editing), you can set the VIEWER environment variable to pg and export VIEWER. cscope will then invoke pg instead of vi.

An environment variable called VPATH can be set to specify directories to be searched for source files. See View Paths.

Step 2: Invoke the cscope Program

By default, cscope builds a symbol cross-reference table for all the C, lex, and yacc source files in the current directory, and for any included header files in the current directory or the standard place. So, if all the source files for the program to be browsed are in the current directory, and if its header files are there or in the standard place, invoke cscope without arguments:

% cscope

To browse through selected source files, invoke cscope with the names of those files as arguments:

% cscope file1.c file2.c file3.h

For other ways to invoke cscope, see Command-Line Options.

cscope builds the symbol cross-reference table the first time it is used on the source files for the program to be browsed. By default, the table is stored in the file cscope.out in the current directory. On a subsequent invocation, cscope rebuilds the cross-reference only if a source file has been modified or the list of source files is different. When the cross-reference is rebuilt, the data for the unchanged files is copied from the old cross-reference, which makes rebuilding faster than the initial build, and reduces startup time for subsequent invocations.

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 9-1   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 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 9-2   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.

Step 4: Edit the Code

On a windowing terminal, you may have multiple windows of arbitrary size. The error message out of storage might have appeared as a result of running prog in a window with too few lines. In other words, that may have been one of the situations in which mymalloc() was called with a negative number. Now you want to be sure that when the program aborts in this situation in the future, it does so after printing the more meaningful error message screen too small. Edit the function dispinit() as follows.

cscope Function: Correcting the Problem:

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

You have fixed the problem we began investigating at the beginning of this section. Now if prog is run in a window with too few lines, it does not simply fail with the unedifying error message out of storage. Instead, it checks the window size and generates a more meaningful error message before exiting.

Command-Line Options

As noted, cscope builds a symbol cross-reference table for the C, lex, and source files in the current directory by default. That is,

% cscope

is equivalent to:

% cscope *.[chly]

We have also seen that you can browse through selected source files by invoking cscope with the names of those files as arguments:

% cscope file1.c file2.c file3.h

cscope provides command-line options with greater flexibility in specifying source files to be included in the cross-reference. When you invoke cscope with the -s option and any number of directory names (separated by commas):

% cscope -s dir1,dir2,dir3

cscope builds a cross-reference for all the source files in the specified directories as well as the current directory. To browse through all of the source files whose names are listed in file (file names separated by spaces, tabs, or new-lines), invoke cscope with the -i option and the name of the file containing the list:

% cscope -i file

If your source files are in a directory tree, use the following commands to browse through all of them:

% find . -name '*.[chly]' -print | sort > file % cscope -i file

If this option is selected, however, cscope ignores any other files appearing on the command-line.

The -I option can be used for cscope in the same way as the -I option to cc. See Include Files.

You can specify a cross-reference file other than the default cscope.out by invoking the -f option. This is useful for keeping separate symbol cross-reference files in the same directory. You may want to do this if two programs are in the same directory, but do not share all the same files:

% cscope -f admin.ref admin.c common.c aux.c libs.c % cscope -f delta.ref delta.c common.c aux.c libs.c

In this example, the source files for two programs, admin and delta, are in the same directory, but the programs consist of different groups of files. By specifying different symbol cross-reference files when you invoke cscope for each set of source files, the cross-reference information for the two programs is kept separate.

You can use the -pn option to specify that cscope display the path name, or part of the path name, of a file when it lists the results of a search. The number you give to -p stands for the last n elements of the path name you want to be displayed. The default is 1, the name of the file itself. So if your current directory is home/common, the command:

% cscope -p2

causes cscope to display common/file1.c, common/file2.c, and so forth when it lists the results of a search.

If the program you want to browse contains a large number of source files, you can use the -b option, so that cscope stops after it has built a cross-reference; cscope does not display a menu of tasks. When you use cscope -b in a pipeline with the batch(1) command, cscope builds the cross-reference in the background:

% echo 'cscope -b' | batch

Once the cross-reference is built, and as long as you have not changed a source file or the list of source files in the meantime, you need only specify:

% cscope

for the cross-reference to be copied and the menu of tasks to be displayed in the normal way. You can use this sequence of commands when you want to continue working without having to wait for cscope to finish its initial processing.

The -d option instructs cscope not to update the symbol cross-reference. You can use it to save time if you are sure that no such changes have been made; cscope does not check the source files for changes.

Note – Use the -d option with care. If you specify -d under the erroneous impression that your source files have not been changed, cscope refers to an outdated symbol cross-reference in responding to your queries.

Check the cscope(1) man page for other command-line options.

View Paths

As we have seen, cscope searches for source files in the current directory by default. When the environment variable VPATH is set, cscope searches for source files in directories that comprise your view path. A view path is an ordered list of directories, each of which has the same directory structure below it.

For example, suppose you are part of a software project. There is an official set of source files in directories below /fs1/ofc. Each user has a home directory (/usr/you). If you make changes to the software system, you may have copies of just those files you are changing in /usr/you/src/cmd/prog1. The official versions of the entire program can be found in the directory /fs1/ofc/src/cmd/prog1.

Suppose you use cscope to browse through the three files that comprise prog1, namely, f1.c, f2.c, and f3.c. You would set VPATH to /usr/you and /fs1/ofc and export it, as in:

In a Bourne shell, type:

$ VPATH=/usr/you:/fs1/ofc; export VPATH

In a C shell, type:

% setenv VPATH /usr/you:/fs1/ofc

You then make your current directory /usr/you/src/cmd/prog1, and invoke cscope:

% cscope

The program locates all the files in the view path. In case duplicates are found, cscope uses the file whose parent directory appears earlier in VPATH. Thus, if f2.c is in your directory, and all three files are in the official directory, cscope examines f2.c from your directory, and f1.c and f3.c from the official directory.

The first directory in VPATH must be a prefix of the directory you will be working in, usually $HOME. Each colon-separated directory in VPATH must be absolute: it should begin at /.

cscope and Editor Call Stacks

cscope and editor calls can be stacked. That is, when cscope puts you in the editor to view a reference to a symbol and there is another reference of interest, you can invoke cscope again from within the editor to view the second reference without exiting the current invocation of either cscope or the editor. You can then back up by exiting the most recent invocation with the appropriate cscope and editor commands.

Examples

This section presents examples of how cscope can be used to perform three tasks: changing a constant to a preprocessor symbol, adding an argument to a function, and changing the value of a variable. The first example demonstrates the procedure for changing a text string, which differs slightly from the other tasks on the cscope menu. That is, once you have entered the text string to be changed, cscope prompts you for the new text, displays the lines containing the old text, and waits for you to specify which of these lines you want it to change.

Changing a Constant to a Preprocessor Symbol

Suppose you want to change a constant, 100, to a preprocessor symbol, MAXSIZE. Select the sixth menu item, Change this text string, and enter /100. The 1 must be escaped with a backslash because it has a special meaning (item 1 on the menu) to cscope. Now press Return. cscope prompts you for the new text string. Type MAXSIZE.

cscope Function: Changing a Text String:

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: /100 Find this egrep pattern: Find this file: Find files #including this file: To: MAXSIZE

cscope displays the lines containing the specified text string, and waits for you to select those in which you want the text to be changed.

cscope Function: Prompting for Lines to be Changed:

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: /100 Find this egrep pattern: Find this file: Find files #including this file: To: MAXSIZE

You know that the constant 100 in lines 1, 2, and 3 of the list (lines 4, 26, and 8 of the listed source files) should be changed to MAXSIZE. You also know that 0100 in read.c and 100.0 in err.c (lines 4 and 5 of the list) should not be changed. You select the lines you want changed with the following single-key commands:

TABLE 9-3   Commands for Selecting Lines to be Changed

1-9	Mark or unmark the line to be changed.
*	Mark or unmark all displayed lines to be changed.
Space	Display the next set of lines.
+	Display the next set of lines.
-	Display the previous set of lines.
a	Mark all lines to be changed.
^d	Change the marked lines and exit.
Esc	Exit without changing the marked lines.

In this case, enter 1, 2, and 3. The numbers you type are not printed on the screen. Instead, cscope marks each list item you want to be changed by printing a > (greater than) symbol after its line number in the list.

cscope Function: Marking Lines to be Changed:

Change "100" to "MAXSIZE" File Line 1>init.c 4 char s[100]; 2>init.c 26 for (i = 0; i < 100; i++) 3>find.c 8 if (c < 100) { 4 read.c 12 f = (bb & 0100); 5 err.c 19 p = total/100.0; /* get percentage */ 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: Select lines to change (press the ? key for help):

Now type ^d to change the selected lines. cscope displays the lines that have been changed and prompts you to continue.

cscope Function: Displaying Changed Lines of Text:

Changed lines: char s[MAXSIZE]; for (i = 0; i < MAXSIZE; i++) if (c < MAXSIZE) { Press the RETURN key to continue:

When you press Return in response to this prompt, cscope redraws the screen, restoring it to its state before you selected the lines to be changed.

The next step is to add the #define for the new symbol MAXSIZE. Because the header file in which the #define is to appear is not among the files whose lines are displayed, you must escape to the shell by typing !. The shell prompt appears at the bottom of the screen. Then enter the editor and add the #define.

cscope Function: Exiting to the Shell:

Text string: 100 File Line 1 init.c 4 char s[100]; 2 init.c 26 for (i = 0; i < 100; i++) 3 find.c 8 if (c < 100) { 4 read.c 12 f = (bb & 0100); 5 err.c 19 p = total/100.0; /* get percentage */ 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: $ vi defs.h

To resume the cscope session, quit the editor and type ^d to exit the shell.

Adding an Argument to a Function

Adding an argument to a function involves two steps: editing the function itself and adding the new argument to every place in the code where the function is called.

First, edit the function by using the second menu item, Find this global definition. Next, find out where the function is called. Use the fourth menu item, Find functions calling this function, to obtain a list of all the functions that call it. With this list, you can either invoke the editor for each line found by entering the list number of the line individually, or invoke the editor for all the lines automatically by typing ^e. Using cscope to make this kind of change ensures that none of the functions you need to edit are overlooked.

Changing the Value of a Variable

At times, you may want to see how a proposed change affects your code.

Suppose you want to change the value of a variable or preprocessor symbol. Before doing so, use the first menu item, Find this C symbol, to obtain a list of references that are affected. Then use the editor to examine each one. This step helps you predict the overall effects of your proposed change. Later, you can use cscope in the same way to verify that your changes have been made.

Command-Line Syntax for Editors

cscope invokes the vi editor by default. You can override the default setting by assigning your preferred editor to the EDITOR environment variable and exporting EDITOR, as described in Step 1: Set Up the Environment. However, cscope expects the editor it uses to have a command-line syntax of the form:

% editor +linenum filename

as does vi. If the editor you want to use does not have this command-line syntax, you must write an interface between cscope and the editor.

Suppose you want to use ed. Because ed does not allow specification of a line number on the command-line, you cannot use it to view or edit files with cscope unless you write a shell script that contains the following line:

/usr/bin/ed $2

Let's name the shell script myedit. Now set the value of EDITOR to your shell script and export EDITOR:

In a Bourne shell, type:

$ EDITOR=myedit; export EDITOR

In a C shell, type:

% setenv EDITOR myedit

When cscope invokes the editor for the list item you have specified, say, line 17 in main.c, it invokes your shell script with the command-line:

% myedit +17 main.c

myedit then discards the line number ($1) and calls ed correctly with the file name ($2). Of course, you are not moved automatically to line 17 of the file and must execute the appropriate ed commands to display and edit the line.

Unknown Terminal Type Error

If you see the error message:

Sorry, I don't know how to deal with your "term" terminal

your terminal may not be listed in the Terminal Information Utilities (terminfo) database that is currently loaded. Make sure you have assigned the correct value to TERM. If the message reappears, try reloading the Terminal Information Utilities.

If this message is displayed:

Sorry, I need to know a more specific terminal type than "unknown"

set and export the TERM variable as described in Step 1: Set Up the Environment.

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