Q36870: INFO: C2106 Error Assigning a String Literal to a char Array

Article: Q36870
Product(s): Microsoft Programming Utilities
Version(s): 1.0,1.5,6.0,6.0a,6.0ax; MS-DOS:7.0; winnt:1.0,2.0,2.1,4.0,5.0,6.0
Operating System(s): 
Keyword(s): kberrmsg kbLangC kbVC kbVC100 kbVC150 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600
Last Modified: 15-JUN-2001

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The information in this article applies to:

- Microsoft C for MS-DOS, versions 6.0, 6.0a, 6.0ax 
- Microsoft C/C++ for MS-DOS, version 7.0 
- Microsoft Visual C++, version 1.5 
- Microsoft Visual C++, versions 1.0, 2.0, 2.1, 4.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
- Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SUMMARY
=======

A common programming error in C involves an attempt to fill a character array,
declared as "char arrayname[somelength]," with a string constant by using the
simple-assignment operator (the equal sign, "="). This attempt fails and the
compiler generates the following message:

  error C2106: '=' : left operand must be lvalue

Simple assignment works to fill non-auto (global) character arrays and character
pointers (in C version 5.0 and later) with static text. The required
declarations are as follows:

     char string1[10] = "String1";
     char *string2 = "String2";

The text below presents two code examples to demonstrate correct and incorrect
methods to initialize strings.

MORE INFORMATION
================

The following code example does not compile correctly and produces the C2106
error.

Sample Code
-----------

  /*
   * Compile options needed: None
   */ 

  #include <string.h>
  char string1[10];

  void main(void);
  void main(void)
  {
     string1 = "String1";
  }

The following example demonstrates various methods to copy strings.

Sample Code
-----------

  /*
   * Compile options needed: None
   */ 

  /* This example demonstrates some string usage principles. */ 
  #include <stdio.h>
  #include <string.h>
  #include <malloc.h>

  char string1[40];       /* string1 is an array of char  */ 
  char *string2;          /* string2 is a pointer to char */ 
          /* Important: Know when to malloc space for string2. */ 

  void main(void);
  void main(void)
  {
     /* This shows the correct way to achieve the   */ 
     /* assignment intended by string1 = "String1"; */ 
     strcpy(string1, "Contents of string1");
     printf("1:%s\n\n", string1);

     /* These two assignments show two ways to     */ 
     /* use a char pointer with a string literal.  */ 
     string2 = "Contents of string2"; /* point to the literal */ 
     printf("2:%s\n", string2);

     /* allocate memory for char *string2 to point at */ 
     string2 = (char *)malloc(sizeof(string1));
     strcpy(string2, "Contents of string2, again");
     printf("3:%s\n\n", string2);
     free(string2);

     /* This shows a failed attempt to fill a char  */ 
     /* array by assignment through a char pointer. */ 
     string2 = string1;
     string2 = "Contents of string2, but not string1";
     printf("4:%s\n", string1);
     printf("5:%s\n\n", string2);

     /* This shows how correctly to use a pointer   */ 
     /* to fill a char array with a string literal. */ 
     string2 = string1;
     strcpy(string2, "Contents of string2, and also string1");
     printf("6:%s\n", string1);
     printf("7:%s\n\n", string2);
  }

This code generates the following output:

  1:Contents of string1

  2:Contents of string2

  3:Contents of string2, again

  4:Contents of string1
  5:Contents of string2, but not string1

  6:Contents of string2, and also string1
  7:Contents of string2, and also string1

Additional query words:

======================================================================
Keywords          : kberrmsg kbLangC kbVC kbVC100 kbVC150 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbCCompSearch kbZNotKeyword3 kbCComp600DOS kbCComp600aDOS kbCComp600axDOS kbCVC700DOS kbVC500 kbVC600 kbVC200 kbVC210 kbVC32bitSearch kbVC500Search
Version           : :1.0,1.5,6.0,6.0a,6.0ax; MS-DOS:7.0; winnt:1.0,2.0,2.1,4.0,5.0,6.0
Issue type        : kbinfo

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