[英]C strcat - warning: passing arg 2 of `strcat' makes pointer from integer without a cast
I'm having a problem with the program below. 我下面的程序有问题。 I'm trying to scan through a string command entered by the user for certain words. 我正在尝试浏览用户输入的某些单词的字符串命令。 My major issue right now is that when I run the following I get a warning saying that "passing arg 2 of `strcat' makes pointer from integer without a cast". 我现在的主要问题是,当我运行以下命令时,我得到一个警告,即“传递'strcat'的arg 2会使指针从整数开始而没有强制转换”。 My intent is to loop through the first three characters of the string "s", concatenate them onto a string "firstthree", and later check the value of the string "firstthree". 我的意图是遍历字符串“ s”的前三个字符,将它们连接到字符串“ firstthree”,然后检查字符串“ firstthree”的值。 Any help is appreciated. 任何帮助表示赞赏。
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <readline/readline.h>
#include <readline/history.h>
/* Simple example of using gnu readline to get lines of input from a user.
Needs to be linked with -lreadline -lcurses
add_history tells the readline library to add the line to it's
internal histiry, so that using up-arrow (or ^p) will allows the user
to see/edit previous lines.
*/
int main(int argc, char **argv) {
char *s;
while (s=readline("Enter Name: ")) {
add_history(s); /* adds the line to the readline history buffer */
printf("Hello %s\n",s);/*output message to the user*/
char *firstthree;
int i;
for(i = 0; i < 3; i++){
strcat(firstthree, s[i]);
printf("Hello %s\n",firstthree);//checking to see the character added to the end of the string
}
printf("Hey %s\n",firstthree);/*prints out the first three characters*/
free(s); /* clean up! */
free(firstthree);
}
return(0);
}
Your program has a lot of problems; 您的程序有很多问题; you never initialize firstthree
, for example. 例如,您永远不会初始化firstthree
。
The reason you're getting the specific error you're seeing is because of this call: 您收到所看到的特定错误的原因是由于此调用:
strcat(firstthree, s[i]);
s
is a char *
, so s[i]
is a char
, but strcat
expects both parameters to be pointers to null-terminated strings. s
是char *
,所以s[i]
是char
,但是strcat
期望两个参数都是指向以null终止的字符串的指针。 What it seems you want is something like: 您似乎想要的是这样的:
char firstthree[4] = { 0 };
for (int i = 0; i < 3; i++)
{
firstthree[i] = s[i];
printf("Hello %s\n", firstthree);
}
You can't use strcat() to do this; 您不能使用strcat()来执行此操作; it requires two char* s as arguments, not a char* and a char. 它需要两个char *作为参数,而不是char *和char。 You could use strncat() if it is available on your platform. 如果您的平台上提供了strncat(),则可以使用它。
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