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How Do Parameter Modifications Inside a Function Affect the Calling Function in C and C ?
How Do Parameter Modifications Inside a Function Affect the Calling Function in C and C ?
Parameter Modification within Functions: Impact on the Caller
When modifying a parameter within a function, it's crucial to understand its effect on the caller. In the presented code snippet:
<br>void trans(double x,double y,double theta,double m,double n)<br>{</p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">m=cos(theta)*x+sin(theta)*y;
n=-sin(theta)*x+cos(theta)*y;}
calling this function with trans(center_x,center_y,angle,xc,yc) doesn't directly modify the values of xc and yc. This occurs because C passes function parameters by value, meaning the function receives a copy of the variables.
To address this, you have two options:
1. In C :
Use references to pass parameters by reference, modifying the original variables within the function:
<br>void trans(double x, double y, double theta, double& m, double& n)<br>{</p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">m=cos(theta)*x+sin(theta)*y;
n=-sin(theta)*x+cos(theta)*y;}
2. In C:
Pass parameters by explicitly passing their addresses using pointers:
<br>void trans(double x, double y, double theta, double<em> m, double</em> n)<br>{</p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">*m=cos(theta)*x+sin(theta)*y;
*n=-sin(theta)*x+cos(theta)*y;}
With these modifications, calling trans(center_x,center_y,angle,xc,yc) will directly update the values of xc and yc. If this behavior is desired, then using references or pointers is necessary to achieve the desired effect.
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