23.1.4 Commands for Controlled Output
During the execution of a command file or a user-defined command, normal gdb output is suppressed; the only output that appears is what is explicitly printed by the commands in the definition. This section describes three commands useful for generating exactly the output you want.
Print text. Nonprinting characters can be included in
text using C escape sequences, such as \n to print a
newline. No newline is printed unless you specify one.
In addition to the standard C escape sequences, a backslash followed
by a space stands for a space. This is useful for displaying a
string with spaces at the beginning or the end, since leading and
trailing spaces are otherwise trimmed from all arguments.
To print and foo = , use the command
echo \ and foo = \ .
A backslash at the end of text can be used, as in C, to continue the command onto subsequent lines. For example,
echo This is some text\n\ which is continued\n\ onto several lines.\n
produces the same output as
echo This is some text\n echo which is continued\n echo onto several lines.\n
- Print the value of expression and nothing but that value: no
newlines, no $nn = . The value is not entered in the
value history either. See Expressions, for more information
- Print the value of expression in format fmt. You can use
the same formats as for
- Print the values of one or more expressions under the control of
the string template. To print several values, make
expressions be a comma-separated list of individual expressions,
which may be either numbers or pointers. Their values are printed as
specified by template, exactly as a C program would do by
executing the code below:
printf (template, expressions...);
printf, ordinary characters in template are printed verbatim, while conversion specification introduced by the % character cause subsequent expressions to be evaluated, their values converted and formatted according to type and style information encoded in the conversion specifications, and then printed.
For example, you can print two values in hex like this:
printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
printfsupports all the standard
Cconversion specifications, including the flags and modifiers between the % character and the conversion letter, with the following exceptions:
- The argument-ordering modifiers, such as 2$, are not supported.
- The modifier * is not supported for specifying precision or width.
- The ' flag (for separation of digits into groups according to
LC_NUMERIC') is not supported.
- The type modifiers hh, j, t, and z are not supported.
- The conversion letter n (as in %n) is not supported.
- The conversion letters a and A are not supported.
Note that the ll type modifier is supported only if the underlying
Cimplementation used to build gdb supports the
long long inttype, and the L type modifier is supported only if
long doubletype is available.
printfsupports simple backslash-escape sequences, such as
\n, \t, \\, \", \a, and \f, that consist of backslash followed by a single character. Octal and hexadecimal escape sequences are not supported.
printfsupports conversion specifications for DFP (Decimal Floating Point) types using the following length modifiers together with a floating point specifier. letters:
- H for printing
- D for printing
- DD for printing
If the underlying
Cimplementation used to build gdb has support for the three length modifiers for DFP types, other modifiers such as width and precision will also be available for gdb to use.
In case there is no such
Csupport, no additional modifiers will be available and the value will be printed in the standard way.
Here's an example of printing DFP types using the above conversion letters:
printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
- Convert the values of one or more expressions under the control of the string template to a command line, and call it.