Common gcc error messages
 

A typical gcc error message looks like this: 

conepainting.c: In function ‘main’:
conepainting.c:30: error: ‘KInchesPerFoot’ undeclared (first use in this function)
"conepainting.c" is the name of the source file, and ":30:" is the line number where the error was located. The "undeclared" error is a common mistake. All variables must be declared before they are used, and if you forget, you'll see this error. It means the compiler didn't find a declaration for a variable prior to its first use. The error can also occur if you spelled the variable name differently in two places. The compiler is "case-sensitive" so "DOG" and "dog" are two different variables; pay careful attention to upper and lower case letters. 


/tmp/ccJiZokm.o: In function `main':
conepainting.c:(.text+0x63): undefined reference to `sqrt'
collect2: ld returned 1 exit status
You forgot to compile with the math library. Provide the "-lm" flag (that's the letter "l" not the numeral "1" to the compiler, like this: 
gcc -lm conepainting.c


no newline at end of file.
Be sure there is a new line with no blank spaces as the last line in the file.

  warning: implicit declaration of function `printf'
You must have a #include <stdio.h> at the top of the file.

  warning: implicit declaration of function `somename'
Usually means you omitted a required #include statement, but it
might also mean that you omitted a function prototype.

 warning: control reaches end of non-void function
You must have a return  statement at the end of  main() or any function that returns a value.

warning: ISO C forbids nested functions
Missing closing brace at end of a function.

warning: ISO C90 forbids mixed declarations and code
This error means you have a declaration after you started writing executable statements. All variable declarations must be placed at start of the function.

warning: double format, different type arg
Usually this means you specified a floating point placeholder
for an integer variable, or vice versa.

warning: ISO C90 does not support the `%lf' printf
The `%lf' placeholder can only be used with scanf, not printf.

error: syntax error before '}' token
was caused by a missing semicolon.

error: syntax error before "if"
was generated by this code segment
  for ( index = 0; index < kNameLen; index++)
  (
      if (isalpha(name[index]) )
because the line after "for" should be open brace, not open paren.

error: syntax error before "numMessages"
was generated by this statement
void sortMessages(message_type list[], numMessages);
because the datatype "int" was missing before numMessages.

error: invalid type argument of `unary *'
The error was on this line
kPricePerFoot * Feet;
but was caused by this line
#define kPricePerFoot 11;
because #define is not supposed to end in semicolon.

error: syntax error before ';' token
The error was on this line
int list[SIZE];
but was caused by this line
#define SIZE 99;
because #define is not supposed to end in semicolon.

invalid operands to binary %
The remainder operator works only on integers. Make sure both dividend and divisor are integers. Example:
number % pow(x,7) won't work because pow() returns a double.

warning: passing arg 2 of `strcpy' makes pointer from integer without a cast
Needs & before variable name.

warning: char format, different type arg (arg 2)
was generated by this statement:
scanf("%s", &numberstring);
because numberstring is an array and doesn't need the ampersand. 

Undefined                       first referenced
 symbol                             in file
pow                                 /var/tmp//cc44C0mS.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status
This is an error from the linker (not the compiler). If the undefined symbol is pow, ceil, or any of the math functions, then you forgot to include the -lm flag on the gcc command.


Segmentation Fault
This runtime error has several common causes.