blocks|key|1057374|text|您需要：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1057375|sprintf(Buffer,"Hello+World");
sprintf(Buffer+%2B+strlen(Buffer),"Good+Morning");
sprintf(Buffer+%2B+strlen(Buffer),"Good+Afternoon");|code-block|syntax|javascript|1057376|当然，你需要你的缓冲区足够大。|1057377|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

You need:

<pre><code>sprintf(Buffer,"Hello World");
sprintf(Buffer + strlen(Buffer),"Good Morning");
sprintf(Buffer + strlen(Buffer),"Good Afternoon");
</code></pre>

and of course you need your buffer to be big enough.

blocks|key|1057426|text|int+length+=+0;
length+%2B=+sprintf(Buffer%2Blength,+"Hello+World");
length+%2B=+sprintf(Buffer%2Blength,+"Good+Morning");
length+%2B=+sprintf(Buffer%2Blength,+"Good+Afternoon");|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1057427|这是一个对错误有一定抵抗力的版本。如果你不关心什么时候发生错误，这是很有用的，只要你能在错误发生的时候继续你的快乐之路。|unstyled|1057428|int+bytes_added(+int+result_of_sprintf+)
{
++++return+(result_of_sprintf+>+0)+?+result_of_sprintf+:+0;
}

int+length+=+0;
length+%2B=+bytes_added(sprintf(Buffer%2Blength,+"Hello+World"));
length+%2B=+bytes_added(sprintf(Buffer%2Blength,+"Good+Morning"));
length+%2B=+bytes_added(sprintf(Buffer%2Blength,+"Good+Afternoon"));|1057429|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>int length = 0;
length += sprintf(Buffer+length, "Hello World");
length += sprintf(Buffer+length, "Good Morning");
length += sprintf(Buffer+length, "Good Afternoon");
</code></pre>

Here is a version with some resistance to errors. It is useful if you do not care when errors happen so long as you can continue along your merry way when they do.

<pre><code>int bytes_added( int result_of_sprintf )
{
 return (result_of_sprintf &gt; 0) ? result_of_sprintf : 0;
}

int length = 0;
length += bytes_added(sprintf(Buffer+length, "Hello World"));
length += bytes_added(sprintf(Buffer+length, "Good Morning"));
length += bytes_added(sprintf(Buffer+length, "Good Afternoon"));
</code></pre>

blocks|key|1272367|text|snprintf()的snprintfcat()包装器|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1272368|size_t+
snprintfcat(
++++char*+buf,
++++size_t+bufSize,
++++char+const*+fmt,
++++...)
{
++++size_t+result;
++++va_list+args;
++++size_t+len+=+strnlen(+buf,+bufSize);

++++va_start(+args,+fmt);
++++result+=+vsnprintf(+buf+%2B+len,+bufSize+-+len,+fmt,+args);
++++va_end(+args);

++++return+result+%2B+len;
}|code-block|syntax|javascript|1272369|entityMap^0|0|A|B|D|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

A <code>snprintfcat()</code> wrapper for <code>snprintf()</code>:

<pre><code>size_t 
snprintfcat(
 char* buf,
 size_t bufSize,
 char const* fmt,
 ...)
{
 size_t result;
 va_list args;
 size_t len = strnlen( buf, bufSize);

 va_start( args, fmt);
 result = vsnprintf( buf + len, bufSize - len, fmt, args);
 va_end( args);

 return result + len;
}
</code></pre>

blocks|key|1057765|text|使用sprintf()的返回值|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1057766|Buffer+%2B=+sprintf(Buffer,"Hello+World");
Buffer+%2B=+sprintf(Buffer,"Good+Morning");
Buffer+%2B=+sprintf(Buffer,"Good+Afternoon");|code-block|syntax|javascript|1057767|entityMap^0|2|9|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Use the return value of <code>sprintf()</code>

<pre><code>Buffer += sprintf(Buffer,"Hello World");
Buffer += sprintf(Buffer,"Good Morning");
Buffer += sprintf(Buffer,"Good Afternoon");
</code></pre>

blocks|key|1272210|text|当有专门用于您需要的方法(如strcat和strncat+)时，为什么还要使用sprintf进行字符串连接|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1272211|entityMap|0|LINK|mutability|MUTABLE|url|http://www.cplusplus.com/reference/clibrary/cstring/strcat/|1|http://www.cplusplus.com/reference/clibrary/cstring/strncat/^0|E|6|L|7|13|7|E|6|0|L|7|1|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@$9|W|A|X|1|Y]|$9|Z|A|10|1|11]]|E|$]]|$1|F|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]|N|$5|I|J|K|E|$L|O]]]]

Why do you want to use <code>sprintf</code> for string concatenation when there are methods intended specifically for what you need such as <a href="http://www.cplusplus.com/reference/clibrary/cstring/strcat/" rel="noreferrer"><code>strcat</code></a> and <a href="http://www.cplusplus.com/reference/clibrary/cstring/strncat/" rel="noreferrer"><code>strncat</code></a>?

blocks|key|1272562|text|我想你是在找fmemopen(3)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1272563|#include+<assert.h>
#include+<stdio.h>

int+main(void)
{
++++char+buf[128]+=+{+0+};
++++FILE+*fp+=+fmemopen(buf,+sizeof(buf),+"w");

++++assert(fp);

++++fprintf(fp,+"Hello+World!\n");
++++fprintf(fp,+"%25s+also+work,+of+course.\n",+"Format+specifiers");
++++fclose(fp);

++++puts(buf);
++++return+0;
}|code-block|syntax|javascript|1272564|如果动态存储更适合您的用例，您可以遵循Liam关于使用open_memstream(3)的优秀建议|1272565|#include+<assert.h>
#include+<stdio.h>
#include+<stdlib.h>

int+main(void)
{
++++char+*buf;
++++size_t+size;
++++FILE+*fp+=+open_memstream(&buf,+&size);

++++assert(fp);

++++fprintf(fp,+"Hello+World!\n");
++++fprintf(fp,+"%25s+also+work,+of+course.\n",+"Format+specifiers");
++++fclose(fp);

++++puts(buf);
++++free(buf);
++++return+0;
}|1272566|entityMap^0|6|B|0|0|R|H|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

I think you are looking for <code>fmemopen(3)</code>:

<pre><code>#include &lt;assert.h&gt;
#include &lt;stdio.h&gt;

int main(void)
{
 char buf[128] = { 0 };
 FILE *fp = fmemopen(buf, sizeof(buf), "w");

 assert(fp);

 fprintf(fp, "Hello World!\n");
 fprintf(fp, "%s also work, of course.\n", "Format specifiers");
 fclose(fp);

 puts(buf);
 return 0;
}
</code></pre>

If dynamic storage is more suitable for you use-case you could follow Liam's excellent suggestion about using <code>open_memstream(3)</code>:

<pre><code>#include &lt;assert.h&gt;
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;

int main(void)
{
 char *buf;
 size_t size;
 FILE *fp = open_memstream(&amp;buf, &amp;size);

 assert(fp);

 fprintf(fp, "Hello World!\n");
 fprintf(fp, "%s also work, of course.\n", "Format specifiers");
 fclose(fp);

 puts(buf);
 free(buf);
 return 0;
}
</code></pre>

blocks|key|1057558|text|您只是简单地添加字符串文字吗？还是要追加各种数据类型(整型、浮点型等)？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1057559|将其抽象到自己的函数中可能更容易(以下假设为C99)：|1057560|#include+<stdio.h>
#include+<stdarg.h>
#include+<string.h>

int+appendToStr(char+*target,+size_t+targetSize,+const+char+*+restrict+format,+...)
{
++va_list+args;
++char+temp[targetSize];
++int+result;

++va_start(args,+format);
++result+=+vsnprintf(temp,+targetSize,+format,+args);
++if+(result+!=+EOF)
++{
++++if+(strlen(temp)+%2B+strlen(target)+>+targetSize)
++++{
++++++fprintf(stderr,+"appendToStr:+target+buffer+not+large+enough+to+hold+additional+string");
++++++return+0;
++++}
++++strcat(target,+temp);
++}
++va_end(args);
++return+result;
}|code-block|syntax|javascript|1057561|你可以这样使用它：|1057562|char+target[100]+=+{0};
...
appendToStr(target,+sizeof+target,+"%25s+%25d+%25f\n",+"This+is+a+test",+42,+3.14159);
appendToStr(target,+sizeof+target,+"blah+blah+blah");|1057563|等。|1057564|该函数返回来自vsprintf的值，在大多数实现中，该值是写入目标的字节数。这个实现中有一些漏洞，但它应该会给你一些想法。|offset|length|style|CODE|1057565|entityMap^0|0|0|0|0|0|0|7|8|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|12|8|@$Q|13|R|14|S|T]]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

Are you simply appending string literals? Or are you going to be appending various data types (ints, floats, etc.)? 

It might be easier to abstract this out into its own function (the following assumes C99):

<pre><code>#include &lt;stdio.h&gt;
#include &lt;stdarg.h&gt;
#include &lt;string.h&gt;

int appendToStr(char *target, size_t targetSize, const char * restrict format, ...)
{
 va_list args;
 char temp[targetSize];
 int result;

 va_start(args, format);
 result = vsnprintf(temp, targetSize, format, args);
 if (result != EOF)
 {
 if (strlen(temp) + strlen(target) &gt; targetSize)
 {
 fprintf(stderr, "appendToStr: target buffer not large enough to hold additional string");
 return 0;
 }
 strcat(target, temp);
 }
 va_end(args);
 return result;
}
</code></pre>

And you would use it like so:

<pre><code>char target[100] = {0};
...
appendToStr(target, sizeof target, "%s %d %f\n", "This is a test", 42, 3.14159);
appendToStr(target, sizeof target, "blah blah blah");
</code></pre>

etc.

The function returns the value from <code>vsprintf</code>, which in most implementations is the number of bytes written to the destination. There are a few holes in this implementation, but it should give you some ideas.

blocks|key|1272418|text|我发现下面的方法效果很好。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1272419|sprintf(Buffer,"Hello+World");
sprintf(&Buffer[strlen(Buffer)],"Good+Morning");
sprintf(&Buffer[strlen(Buffer)],"Good+Afternoon");|code-block|syntax|javascript|1272420|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I find the following method works nicely.
<pre><code>sprintf(Buffer,&quot;Hello World&quot;);
sprintf(&amp;Buffer[strlen(Buffer)],&quot;Good Morning&quot;);
sprintf(&amp;Buffer[strlen(Buffer)],&quot;Good Afternoon&quot;);
</code></pre>

blocks|key|1272490|text|您可以使用如下所示的简单行在一个缓冲区中追加字符串：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1272491|sprintf(Buffer,"%25s+%25s+%25s","Hello+World","Good+Morning","Good+Afternoon");|code-block|syntax|javascript|1272492|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can use the simple line shown below to append strings in one buffer:

<pre><code>sprintf(Buffer,"%s %s %s","Hello World","Good Morning","Good Afternoon");
</code></pre>

blocks|key|1057821|text|使用strcat+http://www.cplusplus.com/reference/cstring/strcat/|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1057822|int+main+()
++++{
++++++char+str[80];
++++++strcpy+(str,"these+");
++++++strcat+(str,"strings+");
++++++strcat+(str,"are+");
++++++strcat+(str,"concatenated.");
++++++puts+(str);
++++++return+0;
++++}




++++Output:


++++these+strings+are+concatenated.+|code-block|syntax|javascript|1057823|entityMap|0|LINK|mutability|MUTABLE|url|http://www.cplusplus.com/reference/cstring/strcat/^0|9|1E|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Use strcat <a href="http://www.cplusplus.com/reference/cstring/strcat/" rel="nofollow">http://www.cplusplus.com/reference/cstring/strcat/</a>

<pre><code>int main ()
 {
 char str[80];
 strcpy (str,"these ");
 strcat (str,"strings ");
 strcat (str,"are ");
 strcat (str,"concatenated.");
 puts (str);
 return 0;
 }




 Output:


 these strings are concatenated. 
</code></pre>

blocks|key|1057896|text|我写了一个支持动态变量字符串追加的函数，比如PHP+str+append+:+str。str+...。等。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1057897|#include+<stdio.h>
#include+<stdlib.h>
#include+<string.h>
#include+<stdarg.h>

int+str_append(char+**json,+const+char+*format,+...)
{
++++char+*str+=+NULL;
++++char+*old_json+=+NULL,+*new_json+=+NULL;

++++va_list+arg_ptr;
++++va_start(arg_ptr,+format);
++++vasprintf(&str,+format,+arg_ptr);

++++//+save+old+json
++++asprintf(&old_json,+"%25s",+(*json+==+NULL+?+""+:+*json));

++++//+calloc+new+json+memory
++++new_json+=+(char+*)calloc(strlen(old_json)+%2B+strlen(str)+%2B+1,+sizeof(char));

++++strcat(new_json,+old_json);
++++strcat(new_json,+str);

++++if+(*json)+free(*json);
++++*json+=+new_json;

++++free(old_json);
++++free(str);

++++return+0;
}

int+main(int+argc,+char+*argv[])
{
++++char+*json+=+NULL;

++++/*
++++str_append(&json,+"name:+%25d,+%25d,+%25d",+1,+2,+3);
++++str_append(&json,+"sex:+%25s",+"male");
++++str_append(&json,+"end");
++++str_append(&json,+"");
++++str_append(&json,+"{\"ret\":true}");
++++*/

++++int+i;
++++for+(i+=+0;+i+<+100;+i%2B%2B)+{
++++++++str_append(&json,+"id-%25d",+i);
++++}

++++printf("%25s\n",+json);

++++if+(json)+free(json);

++++return+0;
}|code-block|syntax|javascript|1057898|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I write a function support dynamic variable string append, like PHP str append: str . str . ... etc.

<pre><code>#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;string.h&gt;
#include &lt;stdarg.h&gt;

int str_append(char **json, const char *format, ...)
{
 char *str = NULL;
 char *old_json = NULL, *new_json = NULL;

 va_list arg_ptr;
 va_start(arg_ptr, format);
 vasprintf(&amp;str, format, arg_ptr);

 // save old json
 asprintf(&amp;old_json, "%s", (*json == NULL ? "" : *json));

 // calloc new json memory
 new_json = (char *)calloc(strlen(old_json) + strlen(str) + 1, sizeof(char));

 strcat(new_json, old_json);
 strcat(new_json, str);

 if (*json) free(*json);
 *json = new_json;

 free(old_json);
 free(str);

 return 0;
}

int main(int argc, char *argv[])
{
 char *json = NULL;

 /*
 str_append(&amp;json, "name: %d, %d, %d", 1, 2, 3);
 str_append(&amp;json, "sex: %s", "male");
 str_append(&amp;json, "end");
 str_append(&amp;json, "");
 str_append(&amp;json, "{\"ret\":true}");
 */

 int i;
 for (i = 0; i &lt; 100; i++) {
 str_append(&amp;json, "id-%d", i);
 }

 printf("%s\n", json);

 if (json) free(json);

 return 0;
}
</code></pre>

blocks|key|1057918|text|char+string1[]+=+"test";
char+string2[]+=+"string";
int+len+=+sizeof(string1)+%2B+sizeof(string2);
char+totalString[len];
sprintf(totalString,+"%25s%25s",string1,string2);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1057919|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>char string1[] = "test";
char string2[] = "string";
int len = sizeof(string1) + sizeof(string2);
char totalString[len];
sprintf(totalString, "%s%s",string1,string2);
</code></pre>

blocks|key|1272653|text|使用strcat(buffer，"Your+new+string...here")作为选项。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1272654|entityMap|0|LINK|mutability|MUTABLE|url|https://linux.die.net/man/3/strcat^0|9|6|H|M|2|6|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

Using <a href="https://linux.die.net/man/3/strcat" rel="nofollow noreferrer">strcat</a>(<code>buffer</code>,"<code>Your new string...here</code>"), as an option.

blocks|key|1272271|text|下面是什么：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1272272|char+s[100]+=+"";

sprintf(s,+"%25s%25s",+s,+"s1");

sprintf(s,+"%25s%25s",+s,+"s2");

sprintf(s,+"%25s%25s",+s,+"s3");

printf("%25s",+s);|code-block|syntax|javascript|1272273|但是要考虑到可能的缓冲区流！|1272274|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

What about:

<pre><code>char s[100] = "";

sprintf(s, "%s%s", s, "s1");

sprintf(s, "%s%s", s, "s2");

sprintf(s, "%s%s", s, "s3");

printf("%s", s);
</code></pre>

But take into account possible buffer ovewflows!

I am facing a serious issue with <code>sprintf</code>.
Suppose my code snippet is:
<pre><code>sprintf(Buffer,&quot;Hello World&quot;);
sprintf(Buffer,&quot;Good Morning&quot;);
sprintf(Buffer,&quot;Good Afternoon&quot;);
.
.
.
</code></pre>
Some hundred sprints....
If I do like this, it's getting overwritten.
How can I avoid overwriting using <code>sprintf</code>? If I give a <code>printf</code> at the end I want to see all the lines.

How to append strings using sprintf?

我正面临着一个关于sprintf的严重问题。假设我的代码片段是：sprintf(Buffer,"Hello World");sprintf(Buffer,"Good Morning");sprintf(Buffer,"Good Afternoon");...上百次冲刺...如果我喜欢这样，它就会被覆盖。如何避免使用sprintf覆盖？如果我在最后给出一个printf，我想看到所有的行。

问如何使用sprintf追加字符串？
EN

回答 14

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