空字符串

1. 空字符串

字符串常量的書寫方式是用一對雙引號包圍一串字符，如下所示：

“Hello” “\aWarning!\a” “Line 1\nLine2” “”

字符串常量 (不像字符常量) 可以是空的。即使是空字符串，依然存在作為終止符的 NUL 宇節。

literal [?l?t?r?l]：adj. 文字的，逐字的，無夸張的 string [str??]：n. 線，弦，細繩，一串，一行

2. '\0'

//============================================================================ // Name : '\0' // Author : Yongqiang Cheng // Version : Version 1.0.0 // Copyright : Copyright (c) 2019 Yongqiang Cheng // Description : Hello World in C++, Ansi-style //============================================================================#include <stdio.h> #include <string.h>int main(int argc, char **argv) {char *str_1 = "yong";char *str_2 = "qiang";char *str_3 = "";int len_str1 = 0;int len_str2 = 0;int len_str3 = 0;len_str1 = strlen(str_1);len_str2 = strlen(str_2);len_str3 = strlen(str_3);printf("len_str1 = %d\n", len_str1);printf("len_str2 = %d\n", len_str2);printf("len_str3 = %d\n", len_str3);printf("%s\n", str_1);printf("%s\n", str_2);printf("%s\n", str_3);if ('\0' == *str_3){printf("yongqiang!\n");}return 0; } len_str1 = 4 len_str2 = 5 len_str3 = 0 yong qiangyongqiang!

3. #include <string.h>

//============================================================================ // Name : '\0' // Author : Yongqiang Cheng // Version : Version 1.0.0 // Copyright : Copyright (c) 2019 Yongqiang Cheng // Description : Hello World in C++, Ansi-style //============================================================================#include <stdio.h>int main(int argc, char **argv) {char *str_1 = "yong";char *str_2 = "qiang";char *str_3 = "";int len_str1 = 0;int len_str2 = 0;int len_str3 = 0;len_str1 = strlen(str_1);len_str2 = strlen(str_2);len_str3 = strlen(str_3);printf("len_str1 = %d\n", len_str1);printf("len_str2 = %d\n", len_str2);printf("len_str3 = %d\n", len_str3);printf("%s\n", str_1);printf("%s\n", str_2);printf("%s\n", str_3);if ('\0' == *str_3){printf("yongqiang!\n");}return 0; } 09:02:07 **** Build of configuration Debug for project yongqiang_example **** make all Building file: ../src/yongqiang.c Invoking: GCC C Compiler gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/yongqiang.d" -MT"src/yongqiang.o" -o "src/yongqiang.o" "../src/yongqiang.c" ../src/yongqiang.c: In function ‘main’: ../src/yongqiang.c:21:13: warning: implicit declaration of function ‘strlen’ [-Wimplicit-function-declaration]len_str1 = strlen(str_1);^ ../src/yongqiang.c:21:13: warning: incompatible implicit declaration of built-in function ‘strlen’ ../src/yongqiang.c:21:13: note: include ‘<string.h>’ or provide a declaration of ‘strlen’ Finished building: ../src/yongqiang.cBuilding target: yongqiang_example Invoking: GCC C Linker gcc -o "yongqiang_example" ./src/yongqiang.o Finished building target: yongqiang_example09:02:08 Build Finished (took 515ms) //============================================================================ // Name : '\0' // Author : Yongqiang Cheng // Version : Version 1.0.0 // Copyright : Copyright (c) 2019 Yongqiang Cheng // Description : Hello World in C++, Ansi-style //============================================================================#include <stdio.h> #include <string.h>int main(int argc, char **argv) {char *str_1 = "yong";char *str_2 = "qiang";char *str_3 = "";int len_str1 = 0;int len_str2 = 0;int len_str3 = 0;len_str1 = strlen(str_1);len_str2 = strlen(str_2);len_str3 = strlen(str_3);printf("len_str1 = %d\n", len_str1);printf("len_str2 = %d\n", len_str2);printf("len_str3 = %d\n", len_str3);printf("%s\n", str_1);printf("%s\n", str_2);printf("%s\n", str_3);if ('\0' == *str_3){printf("yongqiang!\n");}return 0; } len_str1 = 4 len_str2 = 5 len_str3 = 0 yong qiangyongqiang!

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