?

第一要則,不要直接點擊”編譯并且運行”,而是應該點擊”編譯(build)”按鈕,這樣可以保證警告不會被忽略,一些警告是非常有用的.

第二要則:有多個錯誤,要先處理最前面的錯誤,因為后面的錯誤可能前面的錯誤引發的.所以修改最前面的錯誤后就可以立即重新編譯,往往可以看到所有的錯誤信息都不見了.

每一條信息是按字母排序，可以按序查找。

格式說明: 每一條錯誤都提供了樣例程序,編譯信息以及必要的說明

編譯信息格式按 文件名，程序行數，編譯錯誤信息組織，例如

E:\chen\dream\ex.c|6|error: break statement not within loop or switch|

使用說明: 使用關鍵字查找本文,如undeclared

?

a label can only be part of a statement and a declaration is not a statement|

break statement not within loop or switch

character constant too long for its type

conflicting types for ‘XXX’

'else' without a previous 'if'

empty character constant

expected declaration or statement at end of input

expected declaration specifiers or '...' before string constant

expected expression before 'X' token

expected primary-expression before '=' token

expected identifier or '(' before '}' token

expected '=', ',', ';', 'asm' or '__attribute__' before 'X' token

expected ';' before ?‘XXX’

expected '(' before '{' token

expected ')' before 'X' token

extra tokens at end of #include directive [enabled by default]|

format '%X' expects argument of type 'XXX',

'gets' is deprecated

implicit declaration of function 'XXX'

incompatible type for argument X of 'XXX

invalid operands to binary X

invalid preprocessing directive 'XXX

invalid suffix "X" on integer constant

lvalue required as left operand of assignment

missing terminating X character

情況一： missing terminating " character 漏掉了右側的雙引號

fatal error: XXX: No such file or directory

redefinition of ?‘XXX’

subscripted value is neither array nor pointer nor vector

suggest parentheses around '&&' within '||'（警告）

suggest parentheses around assignment used as truth value

statement with no effect（警告）

stray '\XXX' in program

too few arguments to function 'XXX'

‘XXX’ undeclared

undefined reference to ‘XXX’

unknown type name 'fioat'

unused variable 'XXX'

?

a label can only be part of a statement and a declaration is not a statement|

標號不應該放在聲明處

#include<stdio.h>

int main(void)

{

backward: //應該放在int語句下面

?int i = 0, n, a[32];

?scanf("%d", &n);

?while(n > 0) {

???a[i] = n % 2;

???i = i + 1;

???n = n / 2;

?}

?for(i--; i >= 0; i--)

???printf("%d", a[i]);

?printf("\n");

?goto backward;

?return 0;

}

E:\chen\dream\ex.c|5|error: a label can only be part of a statement and a declaration is not a statement|

break statement not within loop or switch

break必須在循環或switch里面。如果在if里面，if必須在循環或switch里面。

示例

#include <stdio.h>

int main(void)

{

?int i=1;

?if(i==1)

???break;//在if里面是不可以的

?return 0;

}

E:\chen\dream\ex.c|6|error: break statement not within loop or switch|

character constant too long for its type

#include <stdio.h>

int main()

{

?char *s = 'hello,world\n'; //應該用雙引號

?return 0;

}

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|4|warning: character constant too long for its type [enabled by default]|

E:\chen\dream\ex.c|4|warning: initialization makes pointer from integer without a cast [enabled by default]|

解釋:字符常量才用單引號

conflicting types for ‘XXX’

#include<stdio.h>

#include<math.h>

double pow(int x,int y) //math.h中已經有pow函數，兩者不一致，可以取另外的名字

{

return x*y;

}

int main(void)

{

?pow(3,5);

?return 0;

}

E:\chen\dream\ex.c|3|error: conflicting types for 'pow'|

'else' without a previous 'if'

解釋：else沒有配對的if。

#include <stdio.h>

int main(void)

{

?int year = 3;

?scanf("%d", &year);

?if(year % 7); //此處分號多余，導致后面的else沒有配對

?printf("yes\n");

?else

???printf("no\n");

?return 0;

}

E:\chen\dream\ex.c|8|error: 'else' without a previous 'if'

empty character constant

#include <stdio.h>

int main(void)

{

?char s[10]="123";

?if(s[0] == '') //單引號中間有空格，而不是空的沒有字符

???printf("equal\n");

?return 0;

}

E:\chen\dream\ex.c|5|error: empty character constant|

expected declaration or statement at end of input

#include <stdio.h>

int main()

{

?int a = 3;

?return 0; //后面漏掉}

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|error: expected declaration or statement at end of input|

?

解釋: 程序沒有寫完整,漏掉了大括號。

expected declaration specifiers or '...' before string constant

int a,b;

scanf("%d %d",&a, &b); //連個main函數都沒有

E:\chen\dream\ex.c|2|error: expected declaration specifiers or '...' before string constant|

expected expression before 'X' token

一般是因為寫錯了符號或者漏寫了符號或者多敲了符號

示例一

#include <stdio.h>

int main(void)

{

?int a;

?scanf(%d", &a); //%前面少了雙引號

?return 0;

}

E:\chen\dream\ex.c|5|error: expected expression before '%' token|

示例二

#include <stdio.h>

int main(void)

{

?int a = 3;

?if(a= = 3) ?//==之間不能有空格

???print("yes");

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|6|error: expected expression before '=' token|

E:\chen\dream\ex.c|7|warning: implicit declaration of function 'print' [-Wimplicit-function-declaration]|

E:\chen\dream\ex.c|5|warning: variable 'a' set but not used [-Wunused-but-set-variable]|

||=== Build failed: 1 error(s), 2 warning(s) (0 minute(s), 0 second(s)) ===|

示例三

if(s[i]=='a'||s[i]=='A')||s[i]=='e'||s[i]=='E'||s[i]=='i'||s[i]=='I'||s[i]=='o'||s[i]=='O'||s[i]=='u'||s[i]=='U')

error: expected expression before '||' token

注意'A'的后面多寫了)

expected primary-expression before '=' token

if(l!==l1) //多寫了=

error: expected primary-expression before '=' token

expected identifier or '(' before '}' token

示例一

#include <stdio.h>

int main()

{

?return 0;

}

} //此處括號是多余的

E:\chen\dream\ex.c|7|error: expected identifier or '(' before '}' token|

示例二

#include <stdio.h>

int main();

{ ???????????????//其實是這一行的前面多了分號

?return 0;

}

E:\chen\dream\ex.c|3|error: expected identifier or '(' before '{' token|

expected '=', ',', ';', 'asm' or '__attribute__' before 'X' token

少了或者多寫了符號

示例一

#include <stdio.h>

int main

{ ??//實際是main函數后面少了( )

?return 0;

}

E:\chen\dream\ex.c|3|error: expected '=', ',', ';', 'asm' or '__attribute__' before '{' token|

示例二

include <stdio.h> ?//include前面少了#

int main()

{

?return 0;

}

E:\chen\dream\ex.c|1|error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token|

示例三

#include <stdio.h>

int main(void)

{

?int a

?scanf("%d",&a); //前一行漏掉一個分號

?return 0;

}

E:\chen\dream\ex.c|5|error: expected '=', ',', ';', 'asm' or '__attribute__' before 'scanf'|

示例四

int flag==0; //多寫了一個=

error: expected '=', ',', ';', 'asm' or '__attribute__' before '==' token
???

expected ';' before ?‘XXX’

少了分號

示例一

#include <stdio.h>

int main()

{

?printf("hello,world\n") ?

?return 0; //前一行漏掉一個分號

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|error: expected ';' before 'return'|

E:\chen\dream\ex.c|6|warning: control reaches end of non-void function [-Wreturn-type]|

||=== Build failed: 1 error(s), 1 warning(s) (0 minute(s), 0 second(s)) ===|

原因: 上一行的語句少了分號結束(本例中是printf這一行少了分號,但是編譯器顯示錯誤在return 0這一行).

示例二

#include <stdio.h>

int main(void)

{

?int i;

?for(i=1, i<10; i++) //for語句里面應該恰好有兩個分號，i=1后面應該是分號

???printf("%d",i);

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|warning: value computed is not used [-Wunused-value]|

E:\chen\dream\ex.c|5|error: expected ';' before ')' token|

||=== Build failed: 1 error(s), 1 warning(s) (0 minute(s), 0 second(s)) ===|

expected '(' before '{' token

for{b=1;b<=50;b++} //顯然(被誤寫成了{

error: expected '(' before '{' token

expected ')' before 'X' token

一般是漏掉了)號，但是也有其他情況。

示例一

#include <stdio.h>

int main()

{

?printf("hello,world\n"; ?//此處;前面漏掉了)

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|4|error: expected ')' before ';' token|

E:\chen\dream\ex.c|6|error: expected ';' before '}' token|

E:\chen\dream\ex.c|6|warning: control reaches end of non-void function [-Wreturn-type]|

||=== Build failed: 2 error(s), 1 warning(s) (0 minute(s), 2 second(s)) ===|

示例二

#include <stdio.h>

int main()

{

?int a = 3;

?printf("%d%d"a); ?//a前面有應該逗號把兩個參數分開

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|error: expected ')' before 'a'|

E:\chen\dream\ex.c|5|warning: format '%d' expects a matching 'int' argument [-Wformat]|

E:\chen\dream\ex.c|4|warning: unused variable 'a' [-Wunused-variable]|

||=== Build failed: 1 error(s), 2 warning(s) (0 minute(s), 0 second(s)) ===|

示例三

????printf("GCD=%d LCM=%d",gcd(m,n) lcm(m,n)); //lcm前面應該有逗號

Main.c:24:37: error: expected ')' before 'lcm'

示例四

while(scanf("%d %d",&sum,&n) !EOF){ ?//實際上是!=

extra tokens at end of #include directive [enabled by default]|

#include <stdio.h>#include <stdlib.h.> //每個預處理指令如#include應該單獨占據一行

int main()

{

?return 0;

}

E:\chen\dream\ex.c|1|warning: extra tokens at end of #include directive [enabled by default]|

format '%X' expects argument of type 'XXX',

示例一

#include <stdio.h>

int main()

{

?int a;

?scanf("%d", a); //應該是 &a

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|warning: format '%d' expects argument of type 'int *', but argument 2 has type 'int' [-Wformat]|

E:\chen\dream\ex.c|5|warning: 'a' is used uninitialized in this function [-Wuninitialized]|

||=== Build finished: 0 error(s), 2 warning(s) (0 minute(s), 3 second(s)) ===|

||=== Run: Debug in dream (compiler: GNU GCC Compiler) ===|

解釋: 這個是警告,但是該警告往往是不能忽略,初學者一般是忘記了取址&符號

示例二：

#include <stdio.h>

int main(void)

{

?int a=3, b=4;

?printf("%d%d", a); //兩個%d后面應該有兩個參數，此處只有一個a，缺了b

?return 0;

}

E:\chen\dream\ex.c|5|warning: format '%d' expects a matching 'int' argument [-Wformat]|

'gets' is deprecated

這個警告目前可以忽略，是說不鼓勵使用gets

while(gets(str)!=NULL)

warning: 'gets' is deprecated (declared at /usr/include/stdio.h:638) [-Wdeprecated-declarations]
???

implicit declaration of function 'XXX'

解釋: 缺少函數原型.

如果是調用庫函數,可能沒有包含頭文件,示例沒有加stdio.h.或者寫錯了函數名（例如把scanf寫成Scanf）

如果是自定義的函數,記住調用之前一定要聲明或者定義.

示例一

int main()

{

?int a;

?scanf("%d", &a);

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|4|warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]|

E:\chen\dream\ex.c|4|warning: incompatible implicit declaration of built-in function 'scanf' [enabled by default]|

||=== Build finished: 0 error(s), 2 warning(s) (0 minute(s), 0 second(s)) ===|

||=== Run: Debug in dream (compiler: GNU GCC Compiler) ===|

示例二

#include <stdio.h>

int main(void)

{

?int a=3;

?print("%d",&a); //函數名寫錯

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|warning: implicit declaration of function 'print' [-Wimplicit-function-declaration]|

obj\Debug\ex.o||In function `main':|

E:\chen\dream\ex.c|5|undefined reference to `print'|

||=== Build failed: 1 error(s), 1 warning(s) (0 minute(s), 0 second(s)) ===|

incompatible type for argument X of 'XXX

#include <math.h>

int main()

{

?int a = sqrt("4"); //”4”錯誤

?return 0;

}

E:\chen\dream\ex.c|4|error: incompatible type for argument 1 of 'sqrt'|

d:\program files (x86)\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.7.1\..\..\..\..\include\math.h|157|note: expected 'double' but argument is of type 'char *'|

E:\chen\dream\ex.c|4|warning: unused variable 'a' [-Wunused-variable]|

||=== Build failed: 1 error(s), 1 warning(s) (0 minute(s), 0 second(s)) ===|

解釋:調用函數時實參類型和形參類型不兼容.如示例實參是字符串(指針),而形參是double類型

invalid operands to binary X

#include <stdio.h>

int main(void)

{

?int a;

?scanf("%d"&a);//漏掉了逗號，把&當成二元運算符了

?return 0;

}

E:\chen\dream\ex.c|5|error: invalid operands to binary & (have 'char *' and 'int')|

invalid preprocessing directive 'XXX

#inclede <iostream> //include寫錯了

int main()

{

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c|1|error: invalid preprocessing directive #inclede|

||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

解釋:預處理指令寫錯了.

invalid suffix "X" on integer constant

#include <stdio.h>

int main()

{

?int a = 3, b;

?b = 2a; //本意是2*a

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|error: invalid suffix "a" on integer constant|

E:\chen\dream\ex.c|4|warning: variable 'b' set but not used [-Wunused-but-set-variable]|

E:\chen\dream\ex.c|4|warning: unused variable 'a' [-Wunused-variable]|

||=== Build failed: 1 error(s), 2 warning(s) (0 minute(s), 0 second(s)) ===|

解釋: 編譯器把2a看成一個常數,a就是后綴,但是這個后綴不存在. 如3L, 2.5f的L和f就是合法的后綴.示例的錯誤是初學者有時候犯的,應該寫成2*a.

lvalue required as left operand of assignment

解釋：賦值號的左邊應該是左值（一般而言是變量）

#include <stdio.h>

int main(void)

{

?int a = 3;

?if(a % 3 = 0) //此處實際是==號，誤寫為=

???printf("YES");

?return 0;

}

E:\chen\dream\ex.c|5|error: lvalue required as left operand of assignment|

missing terminating X character

情況一： missing terminating " character 漏掉了右側的雙引號

示例一

#include <stdio.h>

int main()

{

?printf("hello,world\n);//漏掉了右邊的雙引號

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|4|warning: missing terminating " character [enabled by default]|

E:\chen\dream\ex.c|4|error: missing terminating " character|

E:\chen\dream\ex.c|5|error: expected expression before 'return'|

E:\chen\dream\ex.c|6|error: expected ';' before '}' token|

E:\chen\dream\ex.c|6|warning: control reaches end of non-void function [-Wreturn-type]|

||=== Build failed: 3 error(s), 2 warning(s) (0 minute(s), 0 second(s)) ===|

原因: ?字符串少了應該用一對雙引號,示例中右邊的雙引號漏掉了

示例二

#include <stdio.h>

int main(void)

{

?print("yesn\");

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|4|warning: implicit declaration of function 'print' [-Wimplicit-function-declaration]|

E:\chen\dream\ex.c|4|warning: missing terminating " character [enabled by default]|

E:\chen\dream\ex.c|4|error: missing terminating " character|

E:\chen\dream\ex.c|5|error: expected expression before 'return'|

E:\chen\dream\ex.c|6|error: expected ';' before '}' token|

E:\chen\dream\ex.c|6|warning: control reaches end of non-void function [-Wreturn-type]|

||=== Build failed: 3 error(s), 3 warning(s) (0 minute(s), 0 second(s)) ===|

這個錯誤是把\n誤寫為 n\, 然后\起轉義作用和雙引號結合，導致編譯器認為少了一個雙引號

情況二、missing terminating ' character

char a='3; //很明顯少了單引號

printf("%d %d %d\n"'a,b,c);//本例單引號實際上是逗號

情況三：missing terminating > character

#include<stdio.h //很明顯少了>

error: missing terminating > character

fatal error: XXX: No such file or directory

寫錯文件名了，例如有寫成stdio,h的。

示例一

#include <studio.h> //文件名寫錯了,stdio.h

int main()

{

?int a, b;

?scanf("%d%d", &a,&b);

?return 0;

}

E:\chen\dream\ex.c|1|fatal error: studio.h: No such file or directory|

示例二 iostream不要用C提交，而是該用C++提交

#include<iostream>

redefinition of ?‘XXX’

解釋 ?XXX重復定義了

原因: (1) 忘了前面已經使用該名字定義標識符了,解決辦法是使用新的名字即可.

(2)很多同學在已有的程序后面再寫新的程序,導致兩個main出現.解決辦法刪掉原來的或者創建一個新文件來寫新程序.

#include <stdio.h>

int main()

{

?return 0;

}

int main()

{

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\dream\ex.c|6|error: redefinition of 'main'|

E:\dream\ex.c|2|note: previous definition of 'main' was here|

||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

subscripted value is neither array nor pointer nor vector

#include <stdio.h>

int main(void)

{

?int a[3]={1,2,3}, n=4;

?n[2]=1; //a誤寫成n，n不是數組類型，也不是指針，不可以[ ]運算

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|error: subscripted value is neither array nor pointer nor vector|

E:\chen\dream\ex.c|4|warning: variable 'n' set but not used [-Wunused-but-set-variable]|

E:\chen\dream\ex.c|4|warning: unused variable 'a' [-Wunused-variable]|

||=== Build failed: 1 error(s), 2 warning(s) (0 minute(s), 0 second(s)) ===|

suggest parentheses around '&&' within '||'（警告）

#include <stdio.h>

int ?isLeap(int ?year)

{

?if(year % 400 == 0 || year % 4 == 0 && year % 100 != 0)

???return ??1;

?else

???return ??0;

}

int main(void)

{

?return 0;

}

E:\chen\dream\ex.c|4|warning: suggest parentheses around '&&' within '||' [-Wparentheses]|

解釋：&&優先級比||高，為了明確此點，你可以加上括號消除這個警告。如下

if(year % 400 == 0 || (year % 4 == 0 && year % 100 != 0))

suggest parentheses around assignment used as truth value

#include <stdio.h>

int main()

{

?int a = 3;

?if(a = 4) // 此處是否為==而不是=

??printf("equal\n");

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|warning: suggest parentheses around assignment used as truth value [-Wparentheses]|

解釋: 雖然只是警告, 但是對于大部分初學者來說,往往是把等于”==”誤寫為賦值”=”

statement with no effect（警告）

語句沒有作用

示例一

#include <stdio.h>

int main(void)

{

?23; ?//顯然這條語句沒有任何作用，可以刪除

}

E:\chen\dream\ex.c|4|warning: statement with no effect [-Wunused-value]|

示例二

#include <stdio.h>

int main(void)

{

?int n;

?n<=10000&&n>=1;//此表達式應該和if，while之類的結合使用，否則不起作用

?return 0;

}

E:\chen\dream\ex.c|5|warning: statement with no effect [-Wunused-value]|

stray '\XXX' in program

總體來說是程序不認識的符號。

原因有

（1）由于中文輸入法的緣故,使用了中文的標點符號(全角)，比如；，｝，＋,改成英文的標點半角符號就行了(搞不清全角半角的話直接切換到英文輸入環境即可)。

（2）在某個平臺下格式不同的文件拿到OJ提交

示例一

#include <stdio.h>

int main()

{

?int a = 3；//這里分號是全角的

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|4|error: stray '\357' in program|

E:\chen\dream\ex.c|4|error: stray '\274' in program|

E:\chen\dream\ex.c|4|error: stray '\233' in program|

E:\chen\dream\ex.c|5|error: expected ',' or ';' before 'return'|

E:\chen\dream\ex.c|4|warning: unused variable 'a' [-Wunused-variable]|

E:\chen\dream\ex.c|6|warning: control reaches end of non-void function [-Wreturn-type]|

||=== Build failed: 4 error(s), 2 warning(s) (0 minute(s), 5 second(s)) ===|

示例二： int main（void） ?//注意這里的括號

示例三

v#include <stdio.h> ?//前面多了一個v，導致#無法識別為預處理指令，#必須在最前面

int main(void)

{

?int a#b; ?//#要么是逗號分成兩個標志符,要么是字母構成一個完整的標識符

?printf("no"\n); ???//\n應該放到雙引號里面

?return 0;

}

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|

E:\chen\dream\ex.c|1|error: stray '#' in program|

E:\chen\dream\ex.c|1|error: unknown type name 'v'|

E:\chen\dream\ex.c|1|error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token|

E:\chen\dream\ex.c|4|error: stray '#' in program|

E:\chen\dream\ex.c|5|error: stray '\' in program|

||=== Build failed: 5 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

示例四：

??rem=x%2;x=x\2; // 除號寫錯了

error: stray '\' in program

too few arguments to function 'XXX'

#include <stdio.h>

int main()

{

?int a;

?scanf(); ?//scanf里面沒有參數

?return 0;

}

E:\chen\dream\ex.c||In function 'main':|

E:\chen\dream\ex.c|5|error: too few arguments to function 'scanf'|

?

解釋:調用函數是參數個數少了

‘XXX’ undeclared

解釋 你使用了標識符‘XXX’,但是沒有看到它的定義

原因 ?(1)你真正忘記定義變量就直接使用了,本例就是這種情況。

(2)寫錯了變量(標識符)的名字,導致前后不一致,還有注意C語言區分大小寫 .解決辦法是保證前后使用同一個標識符

(3)寫錯了關鍵字,C語言的很多關鍵字都是英文單詞,如continue,return，else等等,寫錯了改正過來即可

(4)把數字0誤寫成字母o

(5)使用了頭文件常量，但是沒有#include頭文件。例如使用EOF，NULL要#include <stdio.h>

示例一

#include <stdio.h>

int main()

{

?a = 3;

?return 0;

}

E:\dream\ex.c ?4 error: 'a' undeclared (first use in this function)|

E:\dream\ex.c ?4 note: each undeclared identifier is reported only once for each function it appears in

?

示例二

#include <stdio.h>

int main(void)

{

?int a = 3;

?if(a % 3 == o) ?//有趣之處數字0誤寫成字母o

???print("yes");

?return 0;

}

E:\chen\dream\ex.c|5|error: 'o' undeclared (first use in this function)|

undefined reference to ‘XXX’

解釋:

你調用了’xxx’(例子中是print)函數，但是在目標文件中卻找不到它

原因

1 拼錯了函數的名字,尤其要注意大小寫.例子是printf，漏掉了f

2 真正漏掉了這個函數項目中要添加對應的函數(或文件)

3. ?如果出現undefined reference to `WinMain@16' (或main）一般是main的函數名寫錯了,例如誤寫成mian. 還有可能就是程序中沒有main函數.

4. 調用了非標準庫函數，如getch()

示例

#include <stdio.h>

int main()

{

?print("hello,world\n");

?return 0;

}

編譯信息

In function `main':

E:\dream\ex.c 4 ??????undefined reference to `print'

unknown type name 'fioat'

寫錯了類型名

fioat p(float n); //很明顯應該是float

error: unknown type name 'fioat'

unused variable 'XXX'

#include <stdio.h>

int main()

{

?int a = 3; ?//a在后面沒有被用到

?return 0;

}

E:\chen\dream\ex.c|4|warning: unused variable 'a' [-Wunused-variable]|

解釋:這是一個警告,如果一個變量未使用,意味著刪掉它對程序沒有影響.不刪掉也可以,只是多余而已.

?

||=== Build: Debug in dream (compiler: GNU GCC Compiler) ===|
E:\chen\dream\main.cpp||In function 'SElemType GetTop(SqStack)':|
E:\chen\dream\main.cpp|38|warning: control reaches end of non-void function [-Wreturn-type]|
?

轉載于:https://www.cnblogs.com/4bytes/p/5395022.html

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