Question

Hi I was unable to find the cause of the compilation error while trying this code on Visual studio 2008. I was trying to see an example of char* return value by a function .

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static char* getActiveModuleType(void);
void main()
{
char getActiveModuleBuff[128];
//error C2106: '=' : left operand must be l-value
getActiveModuleBuff = getActiveModuleType();
printf("Active module in well formatted (2): %s\n",getActiveModuleBuff);

    exit(0);
 }
 char* getActiveModuleType(void)
 {
char activeModule[128];
int tempBuffLen=0;
int nbActivemodule = 0;
char moduleA        = 1;
char moduleB        = 1;
char moduleC        = 0;
char moduleD        = 1;
int i = 0;
if(moduleA==1) {activeModule[i] ='A'; activeModule[i+1]=','; i= i+2;}
if(moduleB==1) {activeModule[i] ='B'; activeModule[i+1]=','; i= i+2;}
if(moduleC==1) {activeModule[i] ='C'; activeModule[i+1]=','; i= i+2;}
if(moduleD==1) {activeModule[i] ='D'; activeModule[i+1]=','; i= i+2;}

printf(" Active module in : %s\n",activeModule);
//let get get the last ',' value trucated
tempBuffLen = strlen(activeModule);
nbActivemodule = tempBuffLen/2;
if((tempBuffLen == 0) && (nbActivemodule ==0)){
        memcpy(activeModule,"NoActiveModule",14);
        return activeModule;
}
if(activeModule[tempBuffLen-1]==',')
    activeModule[tempBuffLen-1] = '\0';
printf(" Active module in well formatted : %s\n",activeModule);

return activeModule;
}

i am unable to find why this Error C2106 occurs in this code .
Help required.
thanks

Answer 1

char getActiveModuleBuff[128];
getActiveModuleBuff = getActiveModuleType();

You cannot assign a value to an array in C.

Use memcpy to copy an array or strcpy / strncpy to copy a string.

Also in:

 char* getActiveModuleType(void)
 {
     char activeModule[128];
     /* ... */
     return activeModule;
 }

the activeModule array object is destroyed at the end of the function. Accessing it after the function returns is undefined behavior.