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Index > Expression evaluating commands
Supported on windows
Supported on linux
Supported on embedded
Supported on android
print command
Prints the value of a given expression.
Syntax
print [Expression]
print $[Previous value number]
print {[Type]}[Address]
print [First element]@[Element count]
print /[Format] [Expression]
Parameters
Expression
Specifies the expression that will be evaluated and printed. The expression can include references to variables (e.g. i), registers (e.g. $eax) and pseudo-registers (e.g. $pc). Note that if your expression refers to a local variable, you need to ensure that you have selected the correct frame. You can navigate frames using the up and down commands.
Previous value number
When this format is used and i is specified as the previous value number, the print command will repeat the output produced by its i-th invocation.
Type/Address
This format allows explicitly specifying the address of the evaluated expression and can be used as a shortcut to the C/C++ type conversion. E.g. *((int *)p) is equivalent to {int}p
First element/Element count
This form allows interpreting the First element expression as an array of Element count sequential elements. The most common example of it is *argv@argc
Format
If specified, allows overriding the output format used by the command. Valid format specifiers are:
o - octal
x - hexadecimal
u - unsigned decimal
t - binary
f - floating point
a - address
c - char
s - string
Examples
We will demonstrate the print command using a basic C++ program that prints its own command-line arguments:
#include <stdio.h>
int main(int argc, char **argv)
{
for(int i = 0; i < argc; i++)
printf("Arg %d: %s\n", i, argv[i]);
return 0;
}
We will step into the loop and use several forms of print to show the values of various variables:
(gdb) set args arg1 arg2 arg3
(gdb) start
Temporary breakpoint 1 at 0x8048426: file test.c, line 5.
Starting program: /home/bazis/test arg1 arg2 arg3
Temporary breakpoint 1, main (argc=4, argv=0xbffff024) at test.c:5
warning: Source file is more recent than executable.
5
for(int i = 0; i < argc; i++)
(gdb) next
6
printf("Arg %d: %si, argv[i]);
(gdb) print i
$1 = 0
(gdb) print argv[i]
$2 = 0xbffff204 "/home/bazis/test"
(gdb) print /a argv[i]
$3 = 0xbffff204
(gdb) print /s argv[i]
$4 = 0xbffff204 "/home/bazis/test"
(gdb) print /c argv[i]
$5 = 4 '\004'
(gdb) print *argv
$6 = 0xbffff204 "/home/bazis/test"
(gdb) print *argv@argc
$7 = {0xbffff204 "/home/bazis/test", 0xbffff215 "arg1", 0xbffff21a "arg2", 0xbffff21f "arg3"}
(gdb) print {void *}argv@argc
$8 = {0xbffff204, 0xbffff215, 0xbffff21a, 0xbffff21f}
(gdb) print $2
$9 = 0xbffff204 "/home/bazis/test"
(gdb) next
Arg 0: /home/bazis/test
5
for(int i = 0; i < argc; i++)
(gdb) next
6
printf("Arg %d: %si, argv[i]);
(gdb) print $2
$10 = 0xbffff204 "/home/bazis/test"
(gdb) print argv[i]
$11 = 0xbffff215 "arg1"
(gdb) print /t argv[i]
$12 = 10111111111111111111001000010101
Compatibility with VisualGDB
You can use the print command normally using the GDB Session window in Visual Studio.
See also
Expression evaluating commands ,
display,
set print address,
set print array-indexes,
set print array,
set print elements,
set print frame-arguments, (责任编辑：)
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