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<div class="textblock"><p>Section: <a class="el" href="sec_io.html">Input/Ouput Functions</a> </p>
<h1><a class="anchor" id="Usage"></a>
Usage</h1>
<p>Prints values to the output. The general syntax for its use is </p>
<pre class="fragment"> printf(format,a1,a2,...)
</pre><p> Here <code>format</code> is the format string, which is a string that controls the format of the output. The values of the variables <code>a_i</code> are substituted into the output as required. It is an error if there are not enough variables to satisfy the format string. Note that this <code>printf</code> command is not vectorized! Each variable must be a scalar.</p>
<p>It is important to point out that the <code>printf</code> function does not add a newline (or carriage return) to the output by default. That can lead to some confusing behavior if you do not know what to expect. For example, the command <code>printf('Hello')</code> does not appear to produce any output. In fact, it does produce the text, but it then gets overwritten by the prompt. To see the text, you need <code>printf('Hello<br/>
')</code>. This seems odd, but allows you to assemble a line using multiple <code>printf</code> commands, including the <code>'<br/>
'</code> when you are done with the line. You can also use the <code>'\r'</code> character as an explicit carriage return (with no line feed). This allows you to write to the same line many times (to show a progress string, for example).</p>
<h1><a class="anchor" id="Format"></a>
of the format string</h1>
<p>The format string is a character string, beginning and ending in its initial shift state, if any. The format string is composed of zero or more directives: ordinary characters (not %), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each conversion specification is introduced by the character %, and ends with a conversion specifier. In between there may be (in this order) zero or more flags, an optional minimum field width, and an optional precision.</p>
<p>The arguments must correspond properly (after type promotion) with the conversion specifier, and are used in the order given.</p>
<h1><a class="anchor" id="The"></a>
conversion specifier</h1>
<p>The character <code>%</code> is followed by zero or more of the following flags: </p>
<ul>
<li>
<code>#</code> The value should be converted to an ``alternate form''. For <code>o</code> conversions, the first character of the output string is made zero (by prefixing a <code>0</code> if it was not zero already). For <code>x</code> and <code>X</code> conversions, a nonzero result has the string <code>'0x'</code> (or <code>'0X'</code> for <code>X</code> conversions) prepended to it. For <code>a, A, e, E, f, F, g,</code> and <code>G</code> conversions, the result will always contain a decimal point, even if no digits follow it (normally, a decimal point appears in the results of those conversions only if a digit follows). For <code>g</code> and <code>G</code> conversions, trailing zeros are not removed from the result as they would otherwise be. For other conversions, the result is undefined. </li>
<li>
<code>0</code> The value should be zero padded. For <code>d, i, o, u, x, X, a, A, e, E, f, F, g,</code> and <code>G</code> conversions, the converted value is padded on the left with zeros rather than blanks. If the <code>0</code> and <code>-</code> flags both appear, the <code>0</code> flag is ignored. If a precision is given with a numeric conversion <code>(d, i, o, u, x, and X)</code>, the <code>0</code> flag is ignored. For other conversions, the behavior is undefined. </li>
<li>
<code>-</code> The converted value is to be left adjusted on the field boundary. (The default is right justification.) Except for <code>n</code> conversions, the converted value is padded on the right with blanks, rather than on the left with blanks or zeros. A <code>-</code> overrides a <code>0</code> if both are given. </li>
<li>
<code>' '</code> (a space) A blank should be left before a positive number (or empty string) produced by a signed conversion. </li>
<li>
<code>+</code> A sign (<code>+</code> or <code>-</code>) always be placed before a number produced by a signed conversion. By default a sign is used only for negative numbers. A <code>+</code> overrides a space if both are used. </li>
</ul>
<h1><a class="anchor" id="The"></a>
conversion specifier</h1>
<p>An optional decimal digit string (with nonzero first digit) specifying a minimum field width. If the converted value has fewer characters than the field width, it will be padded with spaces on the left (or right, if the left-adjustment flag has been given). A negative field width is taken as a <code>'-'</code> flag followed by a positive field width. In no case does a non-existent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result.</p>
<h1><a class="anchor" id="The"></a>
conversion specifier</h1>
<p>An optional precision, in the form of a period (<code>'.'</code>) followed by an optional decimal digit string. If the precision is given as just <code>'.'</code>, or the precision is negative, the precision is taken to be zero. This gives the minimum number of digits to appear for <code>d, i, o, u, x</code>, and <code>X</code> conversions, the number of digits to appear after the radix character for <code>a, A, e, E, f</code>, and <code>F</code> conversions, the maximum number of significant digits for <code>g</code> and <code>G</code> conversions, or the maximum number of characters to be printed from a string for s conversions.</p>
<h1><a class="anchor" id="The"></a>
conversion specifier</h1>
<p>A character that specifies the type of conversion to be applied. The conversion specifiers and their meanings are: </p>
<ul>
<li>
<code>d,i</code> The int argument is converted to signed decimal notation. The precision, if any, gives the minimum number of digits that must appear; if the converted value requires fewer digits, it is padded on the left with zeros. The default precision is <code>1</code>. When <code>0</code> is printed with an explicit precision <code>0</code>, the output is empty. </li>
<li>
<code>o,u,x,X</code> The unsigned int argument is converted to unsigned octal (<code>o</code>), unsigned decimal (<code>u</code>), or unsigned hexadecimal (<code>x</code> and <code>X</code>) notation. The letters <code>abcdef</code> are used for <code>x</code> conversions; the letters <code>ABCDEF</code> are used for <code>X</code> conversions. The precision, if any, gives the minimum number of digits that must appear; if the converted value requires fewer digits, it is padded on the left with zeros. The default precision is <code>1</code>. When <code>0</code> is printed with an explicit precision <code>0</code>, the output is empty. </li>
<li>
<code>e,E</code> The double argument is rounded and converted in the style <code>[-]d.ddde dd</code> where there is one digit before the decimal-point character and the number of digits after it is equal to the precision; if the precision is missing, it is taken as <code>6</code>; if the precision is zero, no decimal-point character appears. An <code>E</code> conversion uses the letter <code>E</code> (rather than <code>e</code>) to introduce the exponent. The exponent always contains at least two digits; if the value is zero, the exponent is <code>00</code>. </li>
<li>
<code>f,F</code> The double argument is rounded and converted to decimal notation in the style <code>[-]ddd.ddd</code>, where the number of digits after the decimal-point character is equal to the precision specification. If the precision is missing, it is taken as <code>6</code>; if the precision is explicitly zero, no decimal-point character appears. If a decimal point appears, at least one digit appears before it. </li>
<li>
<code>g,G</code> The double argument is converted in style <code>f</code> or <code>e</code> (or <code>F</code> or <code>E</code> for <code>G</code> conversions). The precision specifies the number of significant digits. If the precision is missing, <code>6</code> digits are given; if the precision is zero, it is treated as <code>1</code>. Style e is used if the exponent from its conversion is less than <code>-4</code> or greater than or equal to the precision. Trailing zeros are removed from the fractional part of the result; a decimal point appears only if it is followed by at least one digit. </li>
<li>
<code>c</code> The int argument is converted to an unsigned char, and the resulting character is written. </li>
<li>
<code>s</code> The string argument is printed. </li>
<li>
<code>%</code> A <code>''</code> is written. No argument is converted. The complete conversion specification is <code>'%'</code>. </li>
</ul>
<h1><a class="anchor" id="Example"></a>
Example</h1>
<p>Here are some examples of the use of <code>printf</code> with various arguments. First we print out an integer and double value.</p>
<pre class="fragment">--> printf('intvalue is %d, floatvalue is %f\n',3,1.53);
intvalue is 3, floatvalue is 1.530000
</pre><p>Next, we print out a string value.</p>
<pre class="fragment">--> printf('string value is %s\n','hello');
string value is hello
</pre><p>Now, we print out an integer using 12 digits, zeros up front.</p>
<pre class="fragment">--> printf('integer padded is %012d\n',32);
integer padded is 000000000032
</pre><p>Print out a double precision value with a sign, a total of 18 characters (zero prepended if necessary), a decimal point, and 12 digit precision.</p>
<pre class="fragment">--> printf('float value is %+018.12f\n',pi);
float value is +0003.141592653590
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