C语言 strcat 在第一个字符串的开头粘贴第二个字符串
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strcat paste second string at beginning of first string
提问by Refael
i use strcat()to connect two strings like:
我strcat()用来连接两个字符串，如：
#include <string.h>
#include <stdio.h>
int main(int argc, char *args[])
{
char *str1; // "456"
char *str2; // "123"
strcat(str1,str2);
printf("%s",str1);
}
i get:
我得到：
456123
but i need the second string on beginning of first string like:
但我需要第一个字符串开头的第二个字符串，例如：
123456
how can i do it ?
我该怎么做 ？
回答by Rohan
Do strcat(str2,str1);, switch the parameters. But you will get resultant string in str2, which you can set to str1if you really want to use str1further in your program.
做strcat(str2,str1);，切换参数。但是你会得到结果字符串 in str2，str1如果你真的想str1在你的程序中进一步使用，你可以设置为。
However, you need to take care appropriately for memory space available in str2.
但是，您需要适当注意str2.
If you want to change str1then, do this
如果你想改变，str1那么这样做
char *tmp = strdup(str1);
strcpy(str1, str2); //Put str2 or anyother string that you want at the begining
strcat(str1, tmp); //concatenate previous str1
...
free(tmp); //free the memory
回答by Sornii
try to use this with static sized arrays, works for me in my project.
尝试将它与静态大小的数组一起使用，在我的项目中对我有用。
void strbeg(char* strReceive, char* strInsert)
{
int strInsertLength = strlen(strInsert);
int strReceiveLength = strlen(strReceive);
for(int i = strReceiveLength; i >= 0; i--)
{
strReceive[i + strInsertLength] = strReceive[i];
}
for(int i = 0; i < strInsertLength; i++)
{
strReceive[i] = strInsert[i];
}
}
回答by unxnut
You need to use strcpyinstead of strcat.
您需要使用strcpy而不是strcat.
回答by alk
Verbatim from man strcat:
逐字来自man strcat：
char *strcat(char *dest, const char *src);
DESCRIPTION
The strcat() function appends the src string to the dest string, overwriting the null byte ('\0') at the end of dest, and then adds a terminating null byte. The strings may not overlap, and the dest string must have enough space for the result.
char *strcat(char *dest, const char *src);
描述
strcat() 函数将 src 字符串附加到 dest 字符串，覆盖 dest 末尾的空字节（'\0'），然后添加一个终止空字节。字符串不能重叠，dest 字符串必须有足够的空间用于结果。
As the programmer you need to make sure that the pointer char * destreferences enough valid memory to hold the addtional chars that will be copied from where char* srcpoints to.
作为程序员，您需要确保指针char * dest引用足够的有效内存来保存char将从 wherechar* src指向的附加s 。
To succesfully prefix str1with str2declare them as follows:
为了成功地前缀str1与str2声明它们如下：
char str2[3 + 1] = "123"; // three for "123" plus 1 for the terminating 0
char str1[2 + 3 + 1] = "46"; // 2 for "46" plus 3 for "123" plus 1 for the terminating zero
to actually concatenate the two chararrays do so:
要实际连接两个char数组，请这样做：
strcat(str1, str2);
